Background
Colorectal cancer (CRC) is the third most common malignancy and the second leading cause of cancer death,1 and is a highly heterogeneous disease given its distinctive carcinogenesis pathways.2 Microsatellite instability-high/mismatch repair deficient (MSI-H/dMMR) tumors, accounting for 10% to 15% of all CRC cases, harbor a high tumor mutational burden and neoantigen load due to the deficiency in recognizing and repairing spontaneous mutations. MSI-H/dMMR tumors have been shown to be highly responsive to immune checkpoint inhibitors (ICIs).3
ICIs that target PD-1, PD-L1, and CTLA-4 have reshaped the treatment landscape of numerous tumor types.4,5 In CRC, recent remarkable efforts and encouraging results from clinical trials have enabled the update of ICIs in guidelines.6–8 The robust antitumor effects induced by ICIs and the potential to eradicate micrometastases have encouraged their application in earlier stages of cancers, such as in a neoadjuvant regimen in nonmetastatic cancer. Compared with metastatic disease after resection, the lower degree of systemic immune suppression, the absence of visceral metastases, and a lower tumor burden in nonmetastatic disease may trigger a stronger antitumor effect after neoadjuvant ICI (nICI) treatment.9 Early-phase trials investigating the activity of nICIs in CRC achieved a 60% to 70% pathologic complete response (pCR) rate in patients with MSI-H/dMMR tumors.10,11
Unlike in other types of cancer and even colon cancer, in addition to reducing the tumor burden and improving survival, the distinctive purpose of neoadjuvant therapy in rectal cancer is organ preservation. After neoadjuvant therapy with good response, patients with tumors involving the anal sphincter may have a clear resection margin through sphincter-preserving surgery,12 and those who achieve clinical complete response (cCR) could follow the intensive watch-and-wait approaches in some circumstances.13 Hence, this specific need further underscores the importance of a careful and precise evaluation after neoadjuvant therapy. However, the distinct mechanisms of ICIs have brought some unique treatment response patterns, such as pseudoprogression.14 Some patients identified as having progressive disease (PD) based on preoperative evaluation following ICI treatment were later confirmed to have pronounced and durable responses, and this unique pattern can be observed in both early and metastatic stages.9,15,16 Previous studies also found that the radiologic findings often underestimate the pathologic response, and this radiographic–pathologic disconnection further increases the difficulties in the response evaluation.17,18 Because of the high pCR rate after nICI treatment in patients with MSI-H/dMMR tumors, this underestimation could lead to the identification of pseudoresidue in the response evaluation, which could subsequently mislead clinicians and result in unnecessary sphincter/organ resection.
To this end, we conducted this study to evaluate the response pattern of nICIs compared with conventional neoadjuvant chemoradiotherapy (nCRT) in patients with MSI-H/dMMR rectal cancer and explored the underlying pathologic characteristics. Based on these findings, we proposed a suggested protocol for decision-making after nICI treatment in those patients.
Patients and Methods
Study Population
Patient data were collected from the prospectively maintained institutional database program of colorectal disease at the Sixth Affiliated Hospital of Sun Yat‐sen University. Patients with MSI-H/dMMR locally advanced rectal cancer (LARC) undergoing nICI treatment from December 2018 to December 2021 were included. Inclusion criteria were histopathologically confirmed adenocarcinoma; clinical stage T3–T4 or any T with positive lymph nodes (N+); distal border of tumors within 12 cm of anal margin; MSI-H/dMMR tumor; and receiving ICI agents in a neoadjuvant setting. All included patients with MSI-H/dMMR LARC received nICIs under the program of the collaborating study group of tumor immunotherapy at the Sixth Affiliated Hospital of Sun Yat‐sen University. All patients provided written informed consent to receive nICIs in accordance with the Declaration of Helsinki. To compare nICIs with conventional neoadjuvant regimens, patients with LARC receiving nCRT were included that were matched 1:1 by sex, age, MSI-H/dMMR status, and radiologic clinical response and were receiving treatment at our center from December 2018 to December 2021. The dMMR status was defined as the absence of the expression of ≥1 MMR proteins (MLH1, MSH1, MSH6, and PMS2) in immunohistochemistry staining. MSI-H status was determined by PCR-capillary electrophoresis assay and defined as at least 2 allele shifts among the 5 consensus tumor microsatellite loci, including BAT-25, BAT-26, NR-21, NR-24, and NR-27.19,20 All patients were staged according to the 8th edition of the AJCC staging system.21 The Institutional Review Board of Sun Yat‐sen University approved this study.
Radiologic Evaluation
Radiologic assessments with thoraco-abdominopelvic CT scan and pelvic MRI were completed at baseline, within 7 to 13 days after completing the first half of scheduled cycles, and before surgery. If patients received any cytotoxic therapy prior to ICI treatment, a reassessment by imaging and colonoscopy was mandatory before the first dose of ICIs. All patients had at least 3-time tumor assessments by thoraco-abdominopelvic CT scan or pelvic MRI. Grading for tumor mass followed the AJCC staging system. Suspicious metastatic regional lymph nodes were marked if they were characterized by a short axis (SA) >10 mm or an SA >5 mm accompanying any malignant features, such as irregular border and heterogeneous intensity. Treatment response was first assessed according to RECIST 1.1,22 and was further assessed following the revised iRECIST23 criteria in this study. Briefly, PD was defined as an increase in target lesions or new lesions based on RECIST 1.1, and would be identified as an unconfirmed PD (iUPD) that would require confirmation in the following assessment according to iRECIST, or as a confirmed PD (iCPD) if increased size of existing lesions or new lesions were found.
Endoscopic and Ultrasonic Evaluation
Colonoscopy and endorectal ultrasound were scheduled at baseline and optional at other radiologic evaluation timepoints. The reports and images of the colonoscope and endorectal ultrasound were reviewed by experienced clinicians blinded to the group assignment. The pretreatment and preoperative findings with colonoscopy and endorectal ultrasound were compared to evaluate the treatment response. The endoscopic response was graded according to the modified criteria defined by an expert international consensus committee.24 Briefly, a poor response (++) was diagnosed when the preoperative tumor mass was similar to that prior to treatment, an incomplete response (+) was diagnosed if a shrunken tumor mass was observed, a near complete response (±) was diagnosed when any irregular mucosa, small mucosal nodules, minor mucosal abnormality, superficial ulceration, or mild persisting erythema of the scar was observed, and a complete response (–) was diagnosed if no ulcer, nodularity, flat scars, and telangiectasia was observed. The ultrasonic staging (uT staging) was based on the criteria developed by Hildebrandt and Feifel.25 Details of the assessments can be found in the supplemental eAppendix 1 (available with this article at JNCCN.org).
Pathologic Evaluation
The surgically removed specimens were evaluated and staged according to the AJCC pathologic staging system (pTNM). The response was graded using the AJCC tumor regression grading (TRG) system by board‐certified pathologists, and patients with no residual tumor were identified as having pCR. The slides were reevaluated in this study. The percentage of residual viable tumor was calculated.26 According to previous studies, the histologic features regarding regression and immune activation, including infiltrating lymphocytes, fibrosis, and necrosis, were evaluated and recorded.18,26 The detailed protocol for evaluation is provided in supplemental eAppendix 1. Two independent trained pathologists blinded to patients’ regimens were assigned to evaluate the slide series of resection specimens, and the percentages of fibrosis and necrosis calculated by the individual pathologists were averaged.
Definition of Pseudoprogression and Pseudoresidue
Pseudoprogression was defined as a patient with clinical PD by radiologic assessment but was confirmed as response by pathologic evaluation. Pseudoresidue was defined as a patient with clinical residual tumor by radiologic assessment but was confirmed as pCR by pathologic evaluation.
Statistical Analysis
Individual variables were compared using the Student t test, Mann-Whitney U test, or Fisher exact test according to their types and distributions. Statistical analyses were performed using R version 4.0.5 (R Foundation for Statistical Computing). All tests were 2-sided, and P<.05 was considered statistically significant.
Results
Treatment and Clinical Characteristics
A total of 13 patients treated with nICIs (nICI group) and 1:1 matched controls (nCRT group) were included. All patients in the nICI group received anti–PD-1 agents, and the patients in the nCRT group received 5-FU–based cytotoxic CRT. The detailed regimens are summarized in supplemental eTable 1. The first patient in the nICIs group initiated ICI treatment on September 24, 2019. The median intervals between the first dose of neoadjuvant agents and surgery were 103 and 125 days in the nICI and nCRT groups, respectively. Baseline demographic features, tumor characteristics, and pathologic results are summarized in Figure 1A and Table 1. Of note, despite being matched in clinical response, 7 and 5 patients did not achieve downstaging in radiologic evaluation in the nICI and nCRT groups, respectively.
Clinical characteristics and treatment outcome evaluations. (A) Heat map of patients’ clinical characteristics. Patients were matched by sex, age (by aged before or after 50 years for early-onset or late-onset CRC), dMMR status, and radiologic clinical response (indicated in red type). Endoscopic and ultrasonic responses were graded according to the protocol described in the methods section and in supplemental eAppendix 1. (B) Swimmer’s chart of the status evolution of patients treated by nICIs. Each lane represents a single patient, and the white gaps between 2 colored blocks represents the timepoints of evaluations. Black lines and dot lines indicate the duration of patients’ treatment. Patients’ pathologic response is also shown.
Abbreviations: CR, complete response; dMMR, DNA mismatch repair deficient; F, female; ICI, immune checkpoint inhibitor; M, male; MPR, major pathologic response; NA, not available; nICI, neoadjuvant immune checkpoint inhibitor; PD, progressive disease; pCR, pathologic complete response; PR, partial response; PT, patient; SD, stable disease; TRG, tumor regression grading system.
aFor early-onset, dMMR status, “+” indicates true/positive and “–” indicates false/negative. For downstaging, “+” indicates a good downstaging from stage III and “–” indicates unchanged clinical stage.
bFor endoscopic response, “++” indicates a poor response, “+” indicates an incomplete response, “±” indicates a near-complete response, and “–” indicates a complete response.
cFor ultrasonic response, “++” indicates a poor response, “+” indicates a near-complete response, and “–” indicates a complete response.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Clinical characteristics and treatment outcome evaluations. (A) Heat map of patients’ clinical characteristics. Patients were matched by sex, age (by aged before or after 50 years for early-onset or late-onset CRC), dMMR status, and radiologic clinical response (indicated in red type). Endoscopic and ultrasonic responses were graded according to the protocol described in the methods section and in supplemental eAppendix 1. (B) Swimmer’s chart of the status evolution of patients treated by nICIs. Each lane represents a single patient, and the white gaps between 2 colored blocks represents the timepoints of evaluations. Black lines and dot lines indicate the duration of patients’ treatment. Patients’ pathologic response is also shown.
Abbreviations: CR, complete response; dMMR, DNA mismatch repair deficient; F, female; ICI, immune checkpoint inhibitor; M, male; MPR, major pathologic response; NA, not available; nICI, neoadjuvant immune checkpoint inhibitor; PD, progressive disease; pCR, pathologic complete response; PR, partial response; PT, patient; SD, stable disease; TRG, tumor regression grading system.
aFor early-onset, dMMR status, “+” indicates true/positive and “–” indicates false/negative. For downstaging, “+” indicates a good downstaging from stage III and “–” indicates unchanged clinical stage.
bFor endoscopic response, “++” indicates a poor response, “+” indicates an incomplete response, “±” indicates a near-complete response, and “–” indicates a complete response.
cFor ultrasonic response, “++” indicates a poor response, “+” indicates a near-complete response, and “–” indicates a complete response.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Clinical characteristics and treatment outcome evaluations. (A) Heat map of patients’ clinical characteristics. Patients were matched by sex, age (by aged before or after 50 years for early-onset or late-onset CRC), dMMR status, and radiologic clinical response (indicated in red type). Endoscopic and ultrasonic responses were graded according to the protocol described in the methods section and in supplemental eAppendix 1. (B) Swimmer’s chart of the status evolution of patients treated by nICIs. Each lane represents a single patient, and the white gaps between 2 colored blocks represents the timepoints of evaluations. Black lines and dot lines indicate the duration of patients’ treatment. Patients’ pathologic response is also shown.
Abbreviations: CR, complete response; dMMR, DNA mismatch repair deficient; F, female; ICI, immune checkpoint inhibitor; M, male; MPR, major pathologic response; NA, not available; nICI, neoadjuvant immune checkpoint inhibitor; PD, progressive disease; pCR, pathologic complete response; PR, partial response; PT, patient; SD, stable disease; TRG, tumor regression grading system.
aFor early-onset, dMMR status, “+” indicates true/positive and “–” indicates false/negative. For downstaging, “+” indicates a good downstaging from stage III and “–” indicates unchanged clinical stage.
bFor endoscopic response, “++” indicates a poor response, “+” indicates an incomplete response, “±” indicates a near-complete response, and “–” indicates a complete response.
cFor ultrasonic response, “++” indicates a poor response, “+” indicates a near-complete response, and “–” indicates a complete response.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Clinical Characteristics
After evaluation, patient #5 in the nICI group received a transanal local excision, and patient #13 in the nICI group was assigned to follow the watch-and-wait strategy. In contrast, other patients in both groups underwent standard total mesorectal excision surgery, and 6 patients in each group underwent ileostomy. The Miles operation was undertaken in patient #4 in the nICI group and patient #3 in the nCRT group, as suggested by the multidisciplinary team. Patient #10 in the nICI group died during hospitalization after surgery due to perioperative complications.
Pseudoresidue and Pseudoprogression
Clinical features and treatment outcomes of each patient are illustrated in Figure 1A. A worse response based on colonoscopy and ultrasound could be observed in the nICI group compared with the nCRT group, although the difference was not statistically significant (Figure 1A, Table 1). However, the pathologic evaluation revealed an immensely disparate result. For patients who underwent surgery, those in the nICI group had a significantly higher pCR rate than their counterparts in the nCRT group (11/12 vs 3/13, respectively; P=.003), whereas the response in the nICI group was highly underestimated by radiologic, endoscopic, and ultrasonic evaluations, and only 1 patient was identified as having a cCR, which resulted in a prevalent pseudoresidue (10/13; 76.9%). Moreover, 3 patients (#1, #4, and #10) who achieved pCR were even diagnosed as PD under the RECIST criteria, which resulted in a pseudoprogression with an incidence of 23.1% (3/13). Among them, 1 and 2 patients with PD were iCPD and iUPD according to iRECIST, respectively (Figure 1B). In addition, patients in the nICI group were found to have persistently enlarged lymph nodes during treatments, and new enlarged nodes were found in 4 (30.8%) patients. However, none of the enlarged nodes was confirmed to be metastatic in pathologic evaluation. The representative radiologic and endoscopic images are shown in Figure 2 and supplemental eFigures 1 and 2. This response pattern was not observed in the nCRT group, in which the radiologic response showed a fair consistency with pathologic response. Therefore, we speculated that this response pattern was exclusive for those who received nICIs.
Representative radiologic images of 3 patients with pseudoprogression. (A) For patient #1, the slides of the sagittal section of MRI showed an enlarged involved area by newly presented abscesses, and the hydronephrosis caused by the involvement of the left ureter was also identified during the on-treatment evaluation, and a further progression was observed at the next assessment. (B) The T2-weighted sequences of patient #4 showed a partial response at the on-treatment evaluation, and increased involvement and abscesses can be recognized at the presurgery evaluation. (C) The transverse section of CT of patient #10 showed a partial response at the on-treatment evaluation and increased tumor volume and newly emerged lymph nodes at the presurgery evaluation, accompanied by a partial intestinal obstruction. These patients were later confirmed to achieve pathologic complete response.
Abbreviation: PT, patient.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Representative radiologic images of 3 patients with pseudoprogression. (A) For patient #1, the slides of the sagittal section of MRI showed an enlarged involved area by newly presented abscesses, and the hydronephrosis caused by the involvement of the left ureter was also identified during the on-treatment evaluation, and a further progression was observed at the next assessment. (B) The T2-weighted sequences of patient #4 showed a partial response at the on-treatment evaluation, and increased involvement and abscesses can be recognized at the presurgery evaluation. (C) The transverse section of CT of patient #10 showed a partial response at the on-treatment evaluation and increased tumor volume and newly emerged lymph nodes at the presurgery evaluation, accompanied by a partial intestinal obstruction. These patients were later confirmed to achieve pathologic complete response.
Abbreviation: PT, patient.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Representative radiologic images of 3 patients with pseudoprogression. (A) For patient #1, the slides of the sagittal section of MRI showed an enlarged involved area by newly presented abscesses, and the hydronephrosis caused by the involvement of the left ureter was also identified during the on-treatment evaluation, and a further progression was observed at the next assessment. (B) The T2-weighted sequences of patient #4 showed a partial response at the on-treatment evaluation, and increased involvement and abscesses can be recognized at the presurgery evaluation. (C) The transverse section of CT of patient #10 showed a partial response at the on-treatment evaluation and increased tumor volume and newly emerged lymph nodes at the presurgery evaluation, accompanied by a partial intestinal obstruction. These patients were later confirmed to achieve pathologic complete response.
Abbreviation: PT, patient.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Histopathologic Alterations Underlying Unique Response Pattern in nICI Treatment
We further investigated the pathologic features in the resected specimens to determine the histologic basis of the residual mass that may contribute to the pseudoresidue and pseudoprogression. As illustrated in Figure 3A, the immune-activation–associated features, including lymphocytes, plasma cells, lymphoid aggregates, and tertiary lymphoid structures, were enriched in the tumors of the nICI group, and infiltrated macrophages showed a borderline association with nICI treatment. For features related to tissue repair, fibrosis and neovascularization were also prominent in the nICI group; however, no significant difference in necrosis was observed between the groups. We further compared patients who achieved pCR and near pCR in the groups. The nCRT group showed mild fibrosis and discrete lymphocyte infiltration, and the arranged 4 layers of intestines could be clearly observed (Figure 3B). In contrast, disrupted or indistinguishable architecture attributed to fibrosis, immune infiltrates, and neovascularization were observed in the nICI group, indicating the presence of a robust immune activation and wound-healing process. Notably, patients with pseudoprogression (#1, #4, and #10) were found to have prominently thickened layers of the intestine with blurred architecture enriched with intensive immune activation and fibrosis accompanied by a high degree of neovascularization, which provided the basis for the manifestation of progression in radiologic evaluation (Figure 3C).
Histopathologic evaluation after the neoadjuvant treatment. (A) Heat map of patients’ pathologic features of surgically removed specimens. The color of each cell represents the grades of each feature. For features including plasm cells, macrophages, lymphoid aggregates, tertiary lymphoid structures, “+” indicates the presence of features. The “–” indicates the absence of neovascularization, “++” indicates high level, and “+” indicates low level. The continuous variables were compared by Student t test, and the nominal variables were compared by Fisher exact test. (B) Representative hematoxylin-eosin stained slides of patients achieving pathologic complete response in the neoadjuvant chemoradiotherapy group (original magnification, x2). Mild fibrogenesis and a low density of immune infiltration were found. (C) Representative hematoxylin-eosin stained slides of patients achieving pathologic complete response in the neoadjuvant immune checkpoint inhibitor group (original magnification, x2). Proliferative fibrosis, dense immune infiltrates, tertiary lymphoid structures, and disrupted architectures were found. The high-power fields (original magnification, x40) showed dense infiltration of plasm cells and other lymphocytes, accompanied by neovascularization.
Abbreviations: PT, patient; sig, significance.
*P<0.05; **P<0.01.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Histopathologic evaluation after the neoadjuvant treatment. (A) Heat map of patients’ pathologic features of surgically removed specimens. The color of each cell represents the grades of each feature. For features including plasm cells, macrophages, lymphoid aggregates, tertiary lymphoid structures, “+” indicates the presence of features. The “–” indicates the absence of neovascularization, “++” indicates high level, and “+” indicates low level. The continuous variables were compared by Student t test, and the nominal variables were compared by Fisher exact test. (B) Representative hematoxylin-eosin stained slides of patients achieving pathologic complete response in the neoadjuvant chemoradiotherapy group (original magnification, x2). Mild fibrogenesis and a low density of immune infiltration were found. (C) Representative hematoxylin-eosin stained slides of patients achieving pathologic complete response in the neoadjuvant immune checkpoint inhibitor group (original magnification, x2). Proliferative fibrosis, dense immune infiltrates, tertiary lymphoid structures, and disrupted architectures were found. The high-power fields (original magnification, x40) showed dense infiltration of plasm cells and other lymphocytes, accompanied by neovascularization.
Abbreviations: PT, patient; sig, significance.
*P<0.05; **P<0.01.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Histopathologic evaluation after the neoadjuvant treatment. (A) Heat map of patients’ pathologic features of surgically removed specimens. The color of each cell represents the grades of each feature. For features including plasm cells, macrophages, lymphoid aggregates, tertiary lymphoid structures, “+” indicates the presence of features. The “–” indicates the absence of neovascularization, “++” indicates high level, and “+” indicates low level. The continuous variables were compared by Student t test, and the nominal variables were compared by Fisher exact test. (B) Representative hematoxylin-eosin stained slides of patients achieving pathologic complete response in the neoadjuvant chemoradiotherapy group (original magnification, x2). Mild fibrogenesis and a low density of immune infiltration were found. (C) Representative hematoxylin-eosin stained slides of patients achieving pathologic complete response in the neoadjuvant immune checkpoint inhibitor group (original magnification, x2). Proliferative fibrosis, dense immune infiltrates, tertiary lymphoid structures, and disrupted architectures were found. The high-power fields (original magnification, x40) showed dense infiltration of plasm cells and other lymphocytes, accompanied by neovascularization.
Abbreviations: PT, patient; sig, significance.
*P<0.05; **P<0.01.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Given that some patients receiving nICIs had persistent or newly emerging enlarged lymph nodes, we further assessed the resected nodes. Although no metastatic node was found, the examined nodes in the nICI group were larger than those of the nCRT group (median SA of nodes: 3.35 vs 2.18 mm, respectively; P=.02). In addition, more germinal centers were observed in the nodes of the nICI group, which suggested an immune activation in antigen response.27 These findings suggest that increased germinal centers, along with residual necrosis and fibrogenesis after tumor clearance, may lead to an increase in node size (supplemental eFigure 3).
Significance of Temporal-Sequenced Biologic and Pathologic Evaluation
Recognizing that the true response might be underestimated by radiology, we further explored whether other clues from preoperative examinations could improve the evaluation. Serum tumor markers, including CEA and CA 19-9, are well established in tracking patient response to treatment in CRC, and a reduction of tumor markers after treatment can be recognized as the biologic response.28,29 As shown in supplemental eFigure 4, a dynamic clearance of CEA/CA 19-9 in patients with elevated baseline levels was observed following nICI treatment, which is consistent with the pathologic evaluation, suggesting its potential as a biologic marker in assisting the response evaluation.
Immediate pathologic evaluation of biopsy samples taken during colonoscopy and ultrasonography while on nICI treatment may also provide valuable information. In the nICI group, no malignant evidence was found in the biopsy samples acquired from the last endoscopic evaluation. As shown for patient #10 in Figure 4A, despite the progression indicated by radiologic and endoscopic evaluations (iUPD at the second time point), the forceps biopsy showed a gradual clearance of all visible cancer cells, which was consistent with the true tumor response that was confirmed in the pathologic evaluation after surgery. In addition, patients #5 and #13 underwent ultrasound-guided fine-needle biopsy, which enabled evaluation of the whole layers of lesions that were suspicious in radiologic imaging (Figure 4B). The negative results encouraged the multidisciplinary team to suggest an anal-preserving strategy with transanal local excision and watch-and-wait strategy upon receiving informed consent from the patients.
Dynamic change of histopathologic features during neoadjuvant immunotherapy in 2 representative patients. (A) Representative hematoxylin-eosin stained slides of biopsy samples from patient #10 taken during colonoscopy (original magnification, x4 and [inset] 40x). A gradual clearance of tumor cells was observed in microscopic evaluation, whereas the radiologic and colonoscopic evaluations showed progressive disease. (B) Representative hematoxylin-eosin stained slides of biopsy samples from patient #13 taken during colonoscopy and ultrasound-guided fine-needle aspiration (original magnification, x4 and [inset] 40x). The pathologic assessments with whole-layer evaluation showed a dynamic tumor clearance. This patient was identified as having clinical complete response, and the watch-and-wait strategy was applied.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Dynamic change of histopathologic features during neoadjuvant immunotherapy in 2 representative patients. (A) Representative hematoxylin-eosin stained slides of biopsy samples from patient #10 taken during colonoscopy (original magnification, x4 and [inset] 40x). A gradual clearance of tumor cells was observed in microscopic evaluation, whereas the radiologic and colonoscopic evaluations showed progressive disease. (B) Representative hematoxylin-eosin stained slides of biopsy samples from patient #13 taken during colonoscopy and ultrasound-guided fine-needle aspiration (original magnification, x4 and [inset] 40x). The pathologic assessments with whole-layer evaluation showed a dynamic tumor clearance. This patient was identified as having clinical complete response, and the watch-and-wait strategy was applied.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
Dynamic change of histopathologic features during neoadjuvant immunotherapy in 2 representative patients. (A) Representative hematoxylin-eosin stained slides of biopsy samples from patient #10 taken during colonoscopy (original magnification, x4 and [inset] 40x). A gradual clearance of tumor cells was observed in microscopic evaluation, whereas the radiologic and colonoscopic evaluations showed progressive disease. (B) Representative hematoxylin-eosin stained slides of biopsy samples from patient #13 taken during colonoscopy and ultrasound-guided fine-needle aspiration (original magnification, x4 and [inset] 40x). The pathologic assessments with whole-layer evaluation showed a dynamic tumor clearance. This patient was identified as having clinical complete response, and the watch-and-wait strategy was applied.
Citation: Journal of the National Comprehensive Cancer Network 21, 2; 10.6004/jnccn.2022.7071
These findings highlight the significance of temporal-sequenced biologic and pathologic evaluation in patients treated with nICIs. Based on these findings, we propose a suggested protocol as a reference for decision-making after nICI treatment in biomarker-selected rectal cancer, which emphasizes the significance of multimodal and temporal-sequenced evaluation to motivate the organ preservation strategy in appropriate patients (supplemental eFigure 5).
Discussion
In contrast to other cancers, including colon cancer, sphincter/organ preservation is an urgent need for patients with rectal cancer,30 and thus has constituted a paradigm shift in clinical management.31 The evolution of multimodal treatment strategies has accelerated the watch-and-wait strategy in clinical settings. Patients with MSI-H/dMMR CRC at both nonmetastatic and metastatic stages who experienced an excellent response to ICIs have been recognized as the most promising population to be cured without surgery.6,10,11,32,33 According to reported results of ongoing trials, 60% to 70% of patients with MSI-H/dMMR CRC could achieve pCR after nICI treatments, whereas pCR rates of 13% and 29.9% have been reported in the conventional nCRT and total neoadjuvant therapy groups, respectively.34,35
Due to the pseudoresidue (10/13; 76.9%) and pseudoprogression (3/13; 23.1%) seen in the nICI treatment groups, the higher pCR rate in the patients treated with nICIs did not confer a higher rate of organ preservation. Of the 13 patients in the nICI group, 12 were found to have pCR, 10 underwent a total mesorectal excision, 1 had a permanent colostomy, and 6 received ileostomy, among whom 1 died due to perioperative complications. In the conventional nCRT, the MRI/CT/ultrasound was reported to have a pooled negative predictive value of 42% to 53% in predicting pCR of LARC.36 Regarding nICIs, except for additional obstacles caused by the distinctive response pattern, a much lower negative predictive value is expected (9.1% in this study) because the pCR rate is significantly higher in nICI-treated patients.10,11 Thus, misestimation based on these approaches would lead to unnecessary surgery in a considerable number of patients with pseudoresidue. Previous studies have reported on the unique pattern of response to ICI treatment among metastatic colon and rectal cancers8,37,38 as well as other types of cancer,14,15 demonstrating an estimated 10% to 20% pseudoprogression among patients who underwent ICI treatment. Unlike metastatic diseases, our study demonstrated that tumors achieving pCR could still present as PD, which further underscores the significance of evaluating and understanding this responding pattern.
Due to the functions of T-cell priming and effect exerting, the ICIs induced a systemically immunologic tumor clearance, which is different from the cytotoxic effects of conventional chemotherapies, and thus the response harbored a distinctive histologic characteristic. In other types of cancer, it has been reported that the histologic regression bed could account for the inconsistency between the radiologic and pathologic response.26 In the current study, we also demonstrated that the increased proliferative fibrosis and immune infiltrates compose the residue mass after tumor clearance, which was responsible for the progressive manifestation in examinations. Apart from the tumor-infiltrating lymphocytes, the germinal centers along with the formation of the tertiary lymphoid structure were more frequently observed in the specimens after nICI treatment. A high density of plasma cell infiltrates has been shown to be associated with a better outcome in solid tumors,39 and was also associated with wound healing.40 Given the presence of plasma cells in other types of ICI-treated tumors18,26 and the function of PD-1 in regulating the selection and survival of B cells,41 plasm cells infiltration might be highly involved in the tumor-killing effect after ICI treatment. However, the underlying mechanisms remain to be elucidated. Apart from the primary tumor, tumor-draining lymph nodes have been shown to be another site where ICIs act.42 Of note, we also found an increased size of nonmetastatic lymph nodes in both radiologic and pathologic evaluations.
Many ongoing clinical trials investigating the neoadjuvant use of ICIs in rectal cancer have adopted pathologic response as a study endpoint (ClinicalTrials.gov identifier: NCT04165772). However, as found in this study, it was not rare for disease to present as tumor residue or progression during evaluation in patients who had achieved pCR. Thus, studies using this endpoint that require surgical removal of the rectum might lead to overtreatment and offset the advantage of nICI treatment. As a result, the RECIST working group updated the criteria for ICI therapies.23 Nevertheless, these criteria are also imaging-based and thus suffer from the low negative predictive value of imaging modalities in predicting pCR.36 Colle et al37 also suggested that the updated criteria might not be fully adapted to CRC according to their findings in patients with metastatic disease. Considering that early identification of pseudoprogression and pseudoresidue could help avoid unnecessary resection, developing specific evaluation strategies and criteria before surgery might facilitate the most optimal decision-making.
Recently, Cercek et al32 reported the results of a new phase II clinical trial, which showed that 12 patients with dMMR rectal cancer who received 9 cycles of nICIs (dostarlimab) in 6 months achieved 100% cCR, and the wait-and-watch strategy was applied in these patients. This study further emphasized the significance of organ preservation in nICI therapy. Of interest, no pseudoprogression was found, which might be attributed to the longer duration of treatment applied in the study.32 In our study, most patients underwent 6 cycles of nICIs every 2 weeks, and the treatment duration was 3 months. Similar underestimation of response was reported in 2 other trials, in which the time intervals between nICI initiation and surgery were 6 weeks and 3 months, respectively.10,11 Nevertheless, according to the previously reported clinical trial that studied the 3-month regimen of toripalimab in patients with LARC,11 the incidence of adverse effects was lower than with the 6-month regimen (grade 1–2 treatment-related adverse effects, 59% vs 75%).11,32 Further studies are needed to determine the optimal nICI regimen. Moreover, emerging evidence has demonstrated that most pseudoprogression is observed in the first 3 months of ICI treatment,37,43,44 and a longer period is required to observe response to ICIs. Therefore, we expected that the multimodal evaluation or extended time interval for response evaluation, regardless of the treatment duration, could be a solution to this dilemma (supplemental eFigure 5).
Previous studies have suggested that some biologic markers reflect the true response better than radiologic assessment. The utility of dynamic changes in circulating tumor DNA (ctDNA) in response evaluation has been well reported, as it could directly reflect the residue tumor burden.45 A decreased level of ctDNA strongly indicates a pronounced response and thus may distinguish pseudoprogression.46 Nevertheless, this sequencing-based approach may increase the cost burden and cannot track tumors that lack hotspot mutations. In addition to this promising method, some currently used clinical approaches could also assist response evaluation. Blood-based tumor markers have also been widely used for response evaluation and relapse surveillance in CRC.47 As part of biologic response, reduced levels of CEA and CA 19-9 have been found to correlate with clinical benefits and thus could indicate the pseudoprogression and pseudoresidue in the current study, which could be supported by the study by Colle et al.37 Of note, acquiring pathologic evidence during treatment is always the gold standard for response evaluation. In patients with pseudoprogression, the pathologic–radiologic disconnection was discovered by using biopsy during nICI treatment. The endoscopic biopsy of a suspicious mucosal lesion could provide direct evidence of regression, and the ultrasound-guided fine-needle biopsy could further enable a whole-layer evaluation of the suspicious lesion with high accuracy.48 Furthermore, enlarged nodes seen on radiologic evaluation must be carefully interpreted during nICI treatment, because they could be metastasis-free and a result of immune activation, as opposed to those found during nCRT.49 Together, our findings underscore the importance of multimodal evaluation, which may provide additional evidence to facilitate the identification of patients achieving good response.
This study had some limitations. Long-term survival of the study population could not be analyzed because the follow-up duration for most cases was <1 year. The patients did not receive universal ICI agents, and the subgroup analyses could not be performed to assess the heterogeneity that the different agents might induce. In addition, the relatively low incidence of MSI-H/dMMR tumors in rectal cancer limits the population in which the findings could be applied.50 However, the high frequency of pseudoresidue and pseudoprogression highlights the significance of developing specific evaluation criteria for patients treated with nICIs. Additionally, the suggested protocol is in preliminary form and needs to be further validated and improved in larger cohorts and prospective trials.
Conclusions
This study demonstrated the pseudoresidue and pseudoprogression in response evaluation and the underlying pathologic basis of this unique pattern in nICI-treated rectal cancer. Extra cautions should be taken in evaluating the primary tumor and lymph nodes, because they could represent fibrogenesis and immune activation that may mislead the radiologic evaluation. Given the high pCR rate after nICI treatment, an organ-preservation strategy, including sphincter/organ-preserving surgery and a watch-and-wait approach, might be appropriate for patients without malignant evidence in the multimodal evaluation for treatment response.
Acknowledgments
The authors would like to thank Prof. Peiyi Xie for reviewing the radiologic images.
References
- 1.↑
Sung H, Ferlay J, Siegel RL, et al. Global cancer statistics 2020: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin 2021;71:209–249.
- 2.↑
Nguyen LH, Goel A, Chung DC. Pathways of colorectal carcinogenesis. Gastroenterology 2020;158:291–302.
- 3.↑
Guinney J, Dienstmann R, Wang X, et al. The consensus molecular subtypes of colorectal cancer. Nat Med 2015;21:1350–1356.
- 4.↑
Topalian SL, Drake CG, Pardoll DM. Immune checkpoint blockade: a common denominator approach to cancer therapy. Cancer Cell 2015;27:450–461.
- 5.↑
Chen DS, Mellman I. Oncology meets immunology: the cancer-immunity cycle. Immunity 2013;39:1–10.
- 6.↑
André T, Shiu KK, Kim TW, et al. Pembrolizumab in microsatellite-instability-high advanced colorectal cancer. N Engl J Med 2020;383:2207–2218.
- 7.↑
Overman MJ, McDermott R, Leach JL, et al. Nivolumab in patients with metastatic DNA mismatch repair-deficient or microsatellite instability-high colorectal cancer (CheckMate 142): an open-label, multicentre, phase 2 study. Lancet Oncol 2017;18:1182–1191.
- 8.↑
Ludford K, Cohen R, Svrcek M, et al. Pathological tumor response following immune checkpoint blockade for deficient mismatch repair advanced colorectal cancer. J Natl Cancer Inst 2021;113:208–211.
- 9.↑
Blank CU, Rozeman EA, Fanchi LF, et al. Neoadjuvant versus adjuvant ipilimumab plus nivolumab in macroscopic stage III melanoma. Nat Med 2018;24:1655–1661.
- 10.↑
Chalabi M, Fanchi LF, Dijkstra KK, et al. Neoadjuvant immunotherapy leads to pathological responses in MMR-proficient and MMR-deficient early-stage colon cancers. Nat Med 2020;26:566–576.
- 11.↑
Hu H, Kang L, Zhang J, et al. Neoadjuvant PD-1 blockade with toripalimab, with or without celecoxib, in mismatch repair-deficient or microsatellite instability-high, locally advanced, colorectal cancer (PICC): a single-centre, parallel-group, non-comparative, randomised, phase 2 trial. Lancet Gastroenterol Hepatol 2022;7:38–48.
- 12.↑
Yuval JB, Thompson HM, Garcia-Aguilar J. Organ preservation in rectal cancer. J Gastrointest Surg 2020;24:1880–1888.
- 13.↑
Smith JJ, Strombom P, Chow OS, et al. Assessment of a watch-and-wait strategy for rectal cancer in patients with a complete response after neoadjuvant therapy. JAMA Oncol 2019;5:e185896.
- 14.↑
Borcoman E, Kanjanapan Y, Champiat S, et al. Novel patterns of response under immunotherapy. Ann Oncol 2019;30:385–396.
- 15.↑
Borghaei H, Paz-Ares L, Horn L, et al. Nivolumab versus docetaxel in advanced nonsquamous non-small-cell lung cancer. N Engl J Med 2015;373:1627–1639.
- 16.↑
Amaria RN, Reddy SM, Tawbi HA, et al. Neoadjuvant immune checkpoint blockade in high-risk resectable melanoma. Nat Med 2018;24:1649–1654.
- 17.↑
Cascone T, William WN Jr, Weissferdt A, et al. Neoadjuvant nivolumab or nivolumab plus ipilimumab in operable non-small cell lung cancer: the phase 2 randomized NEOSTAR trial. Nat Med 2021;27:504–514.
- 18.↑
Stein JE, Soni A, Danilova L, et al. Major pathologic response on biopsy (MPRbx) in patients with advanced melanoma treated with anti-PD-1: evidence for an early, on-therapy biomarker of response. Ann Oncol 2019;30:589–596.
- 19.↑
Zou Q, Wang X, Ren D, et al. DNA methylation-based signature of CD8+ tumor-infiltrating lymphocytes enables evaluation of immune response and prognosis in colorectal cancer. J Immunother Cancer 2021;9:e002671.
- 20.↑
Wong YF, Cheung TH, Lo KW, et al. Detection of microsatellite instability in endometrial cancer: advantages of a panel of five mononucleotide repeats over the National Cancer Institute panel of markers. Carcinogenesis 2006;27:951–955.
- 21.↑
Amin MB, Edge SB, Greene FL, et al., eds. AJCC Cancer Staging Manual, 8th ed. New York, NY: Springer; 2017.
- 22.↑
Eisenhauer EA, Therasse P, Bogaerts J, et al. New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1). Eur J Cancer 2009;45:228–247.
- 23.↑
Seymour L, Bogaerts J, Perrone A, et al. iRECIST: guidelines for response criteria for use in trials testing immunotherapeutics. Lancet Oncol 2017;18:e143–152.
- 24.↑
Smith JJ, Chow OS, Gollub MJ, et al. Organ preservation in rectal adenocarcinoma: a phase II randomized controlled trial evaluating 3-year disease-free survival in patients with locally advanced rectal cancer treated with chemoradiation plus induction or consolidation chemotherapy, and total mesorectal excision or nonoperative management. BMC Cancer 2015;15:767.
- 25.↑
Hildebrandt U, Feifel G. Preoperative staging of rectal cancer by intrarectal ultrasound. Dis Colon Rectum 1985;28:42–46.
- 26.↑
Cottrell TR, Thompson ED, Forde PM, et al. Pathologic features of response to neoadjuvant anti-PD-1 in resected non-small-cell lung carcinoma: a proposal for quantitative immune-related pathologic response criteria (irPRC). Ann Oncol 2018;29:1853–1860.
- 28.↑
Nicholson BD, Shinkins B, Mant D. Blood measurement of carcinoembryonic antigen level for detecting recurrence of colorectal cancer. JAMA 2016;316:1310–1311.
- 29.↑
Formica V, Massara MC, Portarena I, et al. Role of CA19.9 in predicting bevacizumab efficacy for metastatic colorectal cancer patients. Cancer Biomark 2009;5:167–175.
- 30.↑
Gani C, Gani N, Zschaeck S, et al. Organ preservation in rectal cancer: the patients’ perspective. Front Oncol 2019;9:318.
- 31.↑
Fokas E, Appelt A, Glynne-Jones R, et al. International consensus recommendations on key outcome measures for organ preservation after (chemo)radiotherapy in patients with rectal cancer. Nat Rev Clin Oncol 2021;18:805–816.
- 32.↑
Cercek A, Lumish M, Sinopoli J, et al. PD-1 blockade in mismatch repair-deficient, locally advanced rectal cancer. N Engl J Med 2022;386:2363–2376.
- 33.↑
Roxburgh CS. Organ preservation in rectal cancer: towards the norm rather than the exception. Br J Surg 2021;108:745–747.
- 34.↑
Lorimer PD, Motz BM, Kirks RC, et al. Pathologic complete response rates after neoadjuvant treatment in rectal cancer: an analysis of the National Cancer Database. Ann Surg Oncol 2017;24:2095–2103.
- 35.↑
Kasi A, Abbasi S, Handa S, et al. Total neoadjuvant therapy vs standard therapy in locally advanced rectal cancer: a systematic review and meta-analysis. JAMA Netw Open 2020;3:e2030097.
- 36.↑
de Jong EA, ten Berge JC, Dwarkasing RS, et al. The accuracy of MRI, endorectal ultrasonography, and computed tomography in predicting the response of locally advanced rectal cancer after preoperative therapy: a metaanalysis. Surgery 2016;159:688–699.
- 37.↑
Colle R, Radzik A, Cohen R, et al. Pseudoprogression in patients treated with immune checkpoint inhibitors for microsatellite instability-high/mismatch repair-deficient metastatic colorectal cancer. Eur J Cancer 2021;144:9–16.
- 38.↑
Michalarea V, Fontana E, Garces AI, et al. Pseudoprogression on treatment with immune-checkpoint inhibitors in patients with gastrointestinal malignancies: case series and short literature review. Curr Probl Cancer 2019;43:487–494.
- 39.↑
Gentles AJ, Newman AM, Liu CL, et al. The prognostic landscape of genes and infiltrating immune cells across human cancers. Nat Med 2015;21:938–945.
- 40.↑
Sîrbulescu RF, Boehm CK, Soon E, et al. Mature B cells accelerate wound healing after acute and chronic diabetic skin lesions. Wound Repair Regen 2017;25:774–791.
- 41.↑
Good-Jacobson KL, Szumilas CG, Chen L, et al. PD-1 regulates germinal center B cell survival and the formation and affinity of long-lived plasma cells. Nat Immunol 2010;11:535–542.
- 42.↑
Salmon H, Idoyaga J, Rahman A, et al. Expansion and activation of CD103(+) dendritic cell progenitors at the tumor site enhances tumor responses to therapeutic PD-L1 and BRAF inhibition. Immunity 2016;44:924–938.
- 43.↑
Zhao P, Li L, Jiang X, et al. Mismatch repair deficiency/microsatellite instability-high as a predictor for anti-PD-1/PD-L1 immunotherapy efficacy. J Hematol Oncol 2019;12:54.
- 44.↑
Diaz LA Jr, Shiu KK, Kim TW, et al. Pembrolizumab versus chemotherapy for microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer (KEYNOTE-177): final analysis of a randomised, open-label, phase 3 study. Lancet Oncol 2022;23:659–670.
- 45.↑
Cabel L, Proudhon C, Romano E, et al. Clinical potential of circulating tumour DNA in patients receiving anticancer immunotherapy. Nat Rev Clin Oncol 2018;15:639–650.
- 46.↑
Goldberg SB, Narayan A, Kole AJ, et al. Early assessment of lung cancer immunotherapy response via circulating tumor DNA. Clin Cancer Res 2018;24:1872–1880.
- 47.↑
Shen D, Wang X, Wang H, et al. Current surveillance after treatment is not sufficient for patients with rectal cancer with negative baseline CEA. J Natl Compr Canc Netw 2022;20:653–662.e3.
- 48.↑
Fernández-Esparrach G, Alberghina N, Subtil JC, et al. Endoscopic ultrasound-guided fine needle aspiration is highly accurate for the diagnosis of perirectal recurrence of colorectal cancer. Dis Colon Rectum 2015;58:469–473.
- 49.↑
Xie Y, Lin J, Wang X, et al. The addition of preoperative radiation is insufficient for lateral pelvic control in a subgroup of patients with low locally advanced rectal cancer: a post hoc study of a randomized controlled trial. Dis Colon Rectum 2021;64:1321–1330.
- 50.↑
Vilar E, Gruber SB. Microsatellite instability in colorectal cancer-the stable evidence. Nat Rev Clin Oncol 2010;7:153–162.
