HSR22-150: Lymph Node Evaluation of Post-Neoadjuvant Rectal Resection Specimens in Rectal Carcinoma

Thanks to the national accreditation program for rectal cancer, expectations and protocols for the diagnosis, resection, and treatment modalities in rectal adenocarcinomas have been established. Neoadjuvant regimens and complete mesenteric resection have proved to reduce the risk of recurrence of colorectal carcinoma significantly. Lymph node retrieval and assessment of rectal specimen post-neoadjuvant therapy pose a challenge to the pathologist as the quantity of lymph node retrieval are lower. Current guidelines have not established a minimum number of lymph nodes for quality assurance. Lymph node metastases are a strong prognostic indicator for adverse outcomes and disease recurrence. Adequate sampling of lymph nodes is crucial to determine the number of positive lymph nodes as an independent prognostic indicator in Stage II colorectal carcinoma, which prompts adjuvant therapy in these patients. This study aimed to assess the average number of lymph nodes in post-neoadjuvant rectal resection specimens. All patients diagnosed with rectal adenocarcinoma treated surgically at our institution between 2016 and 2021 were included in our study. As part of our IRB-approved study, we assessed the clinicopathological staging, the number of lymph nodes retrieved, and the status of the mesorectum. All specimens were grossed by trained pathology assistants following our grossing institutional guidelines. In all cases, the grosser revisited the specimen to retrieve additional lymph nodes if the quantity of harvested lymph nodes was below the minimum of 12 lymph nodes for colon carcinomas. Thirty-seven of the 75 resection specimens were staged > pT3. Sixty percent of the cases (n=22) had preoperative radiation. On average, 14.22 lymph nodes were retrieved in the neoadjuvant group compared to the 17.6 average number of lymph nodes in the group with no presurgical treatment. The percent of lymph nodes uninvolved by metastatic carcinoma was 63% in the neoadjuvant treatment group compared to 94% in the group that did not receive neoadjuvant therapy. Of the cases with presurgical radiotherapy, 31% had < 12 lymph nodes harvested for microscopic evaluation. Accurate assessment of the number of lymph nodes uninvolved by metastatic carcinoma serves as a prognostic indicator. Further studies are needed to establish a minimum quantity of lymph nodes retrieved in pre-surgically treated resection specimens and the percent of lymph nodes uninvolved by metastatic carcinoma.