Background
Thyroid malignancies comprise 4% of all new cancer diagnoses in the United States, and 10% of these patients will develop distant metastases, which most commonly occur at pulmonary and osseous sites.1–4 For those with differentiated thyroid cancers (DTCs; papillary, follicular, oncocytic) and poorly differentiated thyroid cancers (PDTCs), radioiodine can initially serve as an effective treatment, particularly for younger patients with small metastases; however, many will present with or ultimately transition toward radioiodine-refractory (RAIR) disease. Although initial management in this setting may be active surveillance, the median life expectancy for the metastatic RAIR population who do not receive systemic therapy is reported as <5 years.5
Thus, when patients develop progressive or symptomatic disease, kinase inhibitors (KIs) are used, including 2 systemic lines of antiangiogenic KIs available for DTC or PDTC, and targeted therapies are approved for select cases with specific mutations (NTRK, RET, BRAF).6–8
However, although KIs result in improved progression-free survival (PFS), they are not curative for metastatic disease and are associated with frequent drug-related adverse events (AEs), such as hypertension, fatigue, weight loss, diarrhea, and anorexia, with studies showing 98% of patients having an AE and up to 30% of patients requiring medical intervention.7–10 Given these toxicity concerns, it can be desirable to defer medication with modern KIs as long as possible to maintain patient quality of life, highlighting a clinical need for other strategies to improve metastatic disease control for this population.10
In other solid malignancies, for which systemic therapy alone was the previous mainstay of treatment for low-volume metastatic disease, definitive radiotherapy (dRT) has become a new standard management option. There exists a low-volume metastatic disease state, commonly referred to as oligometastatic, between locally confined cancer and widespread distant involvement.11 For patients with oligometastatic disease of various histologies, dRT courses have been shown to provide excellent control and improved disease outcomes with acceptable rates of toxicity.12–14 Likewise for oligoprogressive disease, retrospective studies have demonstrated dRT for limited growing distant sites can help defer escalation of systemic therapy,15,16 a hypothesis now substantiated for patients with oligoprogressive metastatic non–small cell lung cancer by the randomized, controlled, phase II CURB trial.17
Studies have also shown dRT, specifically stereotactic body RT (SBRT), to be effective for metastatic disease traditionally thought of as radioresistant.18 Renal cell carcinoma (RCC), for example, is similar to thyroid cancer in that RCC is poorly sensitive to chemotherapy, often treated with antiangiogenic KIs, and historically considered radioresistant. However, a single-arm phase II trial investigating dRT with SBRT for oligometastatic RCC showed that patients could achieve a median PFS of 2 years, with 82% of patients off systemic therapy at 1 year post-SBRT.19 As such, a recent Delphi consensus guideline now supports the use of SBRT for oligometastatic and oligoprogressive RCC.20
In summary, retrospective and randomized studies have now shown that dRT significantly increases PFS and/or time to new systemic therapy in various cancers, and we hypothesize that dRT can likewise yield favorable outcomes for patients with metastatic DTC and PDTC. The latest 2024 NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Thyroid Cancer discuss the use of external-beam RT in the adjuvant or salvage settings for the postoperative neck, and mention consideration of higher-dose RT for oligometastatic cases in the palliative RT subsection.21 Yet there are limited clinical data supporting this treatment paradigm specifically for metastatic thyroid cancer. Here we report our experience with dRT for patients with oligometastatic and oligoprogressive metastatic thyroid cancer.
Methods
Patient Selection and Data Extraction
We performed a retrospective analysis of patient data available from The University of Texas MD Anderson Cancer Center as approved by the Institutional Review Board. Patients with oligometastatic (≤5 metastatic lesions) or oligoprogressive (≤5 progressing metastatic lesions) thyroid cancer of any histology except anaplastic or medullary were selected. Patient demographics, treatment history (including dates and types of surgery, RT, chemotherapy, and radioactive iodine [RAI] ablation), and disease characteristics (including histology) were collected from the electronic health record. Radiation treatment details recorded included dose, fractionation, start and end date, and treatment type (SBRT, intensity-modulated RT [IMRT]/volumetric modulated arc therapy [VMAT], 3D-conformal, or proton beam therapy). All oligometastatic or oligoprogressive sites were treated within the corresponding dRT. For this study, only treatment courses considered as definitive prescriptions were included, excluding palliative treatments with biologic effective doses (α/β=10; BED10) ≤40 Gy (eg, 30–37.5 Gy in 10–15 fractions, 20–25 Gy in 5 fractions, or 8–16 Gy in 1 fraction).
All patients were required to have completed definitive locoregional treatment to their primary site for inclusion, including initial thyroidectomy. Patients who received postoperative radiation to the thyroid bed were included, but this treatment was not considered a dRT course for the current analysis. Previous local therapy measures for isolated recurrences were permitted, including surgery (such as salvage neck resections for regional recurrences, wedge resections for lung metastases, craniotomies for brain metastases, spine stabilization surgeries, and other metastasectomies) as well as other procedural interventions (eg, cryoablation), as long as those sites were controlled at the time of first dRT for metastatic disease.
Outcomes and Statistical Analyses
The outcomes analyzed included overall survival (OS; from first dRT), PFS (from first dRT), time to progression at any site (from each dRT), local control of treated sites (from each dRT), and time to systemic therapy escalation (from first dRT), calculated per the Kaplan-Meier method and starting from the last date of treatment delivery. Follow-up was calculated via reverse Kaplan-Meier method. Grade 2–5 toxicities were recorded throughout each patient’s history. Disease progression was determined using RECIST version 1.1 criteria, which was assessed with CT scans. Provider-assessed RT-related toxicities from on-treatment weekly management visits and post-RT follow-up visits were recorded using the CTCAE version 5.0 parameters. Toxicities attributable to systemic therapy or other interventions were not encompassed. Cox proportional hazards modeling was used to assess for associations with outcomes.
Tumor Genetics
We retrieved results from somatic genetic testing whenever available. Molecular testing methods included BRAF V600E immunohistochemistry, BRAF/RAS PCR, or next-generation sequencing (NGS). Most NGS assays were performed at MD Anderson Cancer Center, as detailed in Supplementary Table S1 in the supplementary material, available online. Other NGS assays were performed at outside certified laboratories, most frequently Foundation Medicine (n=9), Caris (n=4), Tempus (n=2), and others (n=3).
Results
We identified 119 patients with oligometastatic or oligoprogressive thyroid cancer who received dRT for 344 metastatic sites from June 2005 through April 2024. At the time of first dRT, two-thirds of patients had oligoprogressive disease and one-third had oligometastatic disease. Histologies included 61% papillary, 15% PDTC, 13% follicular, and 10% oncocytic thyroid cancer. Most patients (96%) were documented to have RAIR disease prior to first dRT course: 100 (84%) had received an average of 2 therapeutic I-131 doses (range, 1–4 doses) prior to first dRT (indicating loss of uptake, mixed response, and/or subsequent progression despite RAI), whereas 12% (n=14) initially presented with nonavid disease without uptake. Only 5 (4%) patients received up-front dRT prior to their first therapeutic I-131 for bulky metastatic lesions. A minority of patients received postoperative radiation to the neck (n=33; 28%) and/or had undergone prior local therapy for a recurrent lesion (n=34; 29%) before receiving dRT for metastatic disease. Median age at first dRT was 64 years (range, 56–71 years). Patients had a median of 5.8 years (IQR, 2.7–10.7 years) from initial diagnosis to first dRT. The cohort comprised 53% men and 47% women, with most self-reported as White (76%) (Table 1).
Univariate Analysis of Association of Patient Demographics, dRT Data, and Systemic Therapy Status With Overall Survival
| Variable | n (%) | P Value |
|---|---|---|
| Gender | .32 | |
| Male | 63 (53) | |
| Female | 56 (47) | |
| Race/Ethnicity | .42 | |
| White | 91 (76) | |
| Hispanic | 14 (12) | |
| Asian | 8 (7) | |
| Black | 14 (5) | |
| Therapeutic RAI | ||
| Before dRT | 100 (84) | .64 |
| After dRT | 17 (14) | .30 |
| Treatment intent | .20 | |
| Oligometastatic | 41 (34) | |
| Oligoprogressive | 78 (66) | |
| Histology | .01 | |
| Papillary | 73 (61) | |
| Follicular | 16 (13) | |
| Oncocytic | 12 (10) | |
| Poorly differentiated | 18 (15) | |
| Number of dRT courses | .57 | |
| 1 | 73 (61) | |
| 2 | 25 (21) | |
| 3 | 13 (11) | |
| 4 | 4 (3.5) | |
| 5 | 1 (1) | |
| ≥6 | 3 (2.5) | |
| Total number of treatment sites | .82 | |
| 1 | 45 (38) | |
| 2 | 29 (24) | |
| 3 | 17 (14) | |
| 4 | 12 (10) | |
| 5–10 | 12 (10) | |
| ≥11 | 4 (3.4) | |
| First dRT site | ||
| Thoracic | 76 (64) | .41 |
| Bone | 34 (28.6) | .84 |
| Head/Neck | 4 (3.4) | |
| Brain | 4 (3.4) | |
| Abdominal/Pelvic | 3 (2.5) | |
| Systemic therapy status for each dRT | ||
| Prior | 37 | .92 |
| Ongoing | 53 | .68 |
| Planned continuation after dRT | 48 | .60 |
| Comorbidities | ||
| Hypertension | 36 (30) | .97 |
| Hyperlipidemia | 17 (14) | .35 |
| Renal disease | 8 (7) | .61 |
| Cardiac disease | 12 (10) | .11 |
| Other malignancy | 13 (11) | .31 |
Abbreviations: dRT, definitive radiotherapy; RAI, radioactive iodine.
The median last follow-up date or date of death from initial diagnosis was 11.1 years (95% CI, 8.5–13.6 years) and from date of first dRT was 2.5 years (95% CI, 1.5–3.6 years). Hypofractionated regimens and stereotactic techniques determined by each treating radiation oncologist were used whenever feasible, aiming for more definitive doses associated with durable local control, with the median prescription dose (by BED10) of 72 Gy (IQR, 51–113 Gy). Details of the most used prescriptions are provided in Supplementary Table S2. Of the 207 treatment courses, 133 (64.5%) were delivered via stereotactic technique and 70 (34%) via IMRT/VMAT, with only 2 (1%) via 3D conformal RT and 1 (0.5%) via proton beam therapy.
Some patients had multiple courses of dRT (range, 1–9), and each dRT course involved treating up to 5 different sites (Table 1). The median time interval between dRT courses was 1 year (IQR, 0.4–1.8 years). On average, each patient had 3 sites (range, 1–23) treated over 2 separate courses. Of the 344 dRTs given among 119 patients, 50% were thoracic, 37% bone, 7.5% brain, 4% abdominopelvic locations, and 1.5% upper cervical neck/retropharyngeal metastases.
Overall Survival
OS following first dRT was a median of 8.5 years (95% CI, 5.6–11.4 years) with 81.5% (SE, 4.5%) OS at 3 years and 69.9% (SE, 5.9%) at 5 years. On univariate analyses, there were no associations with patient demographics, number of RAI attempts, number of dRT courses/sites/locations, comorbidities, or systemic therapy status (previous, ongoing, continued after dRT) (Table 1).
However, survival was adversely impacted by older age (P=.003) and histology (P=.005), with multivariable analysis confirming worse outcomes for patients aged ≥65 years (hazard ratio [HR], 3.2; 95% CI, 1.4–7.2; P=.004) and with PDTC histology (HR, 3.04; 95% CI, 1.30–7.1; P=.010). When comparing subtypes, median survival for PDTC histology was 3.6 years (95% CI, 1.7–5.5 years) versus 8.5 years (95% CI, 5.6–11.5 years) for differentiated tumors (log-rank P=.003) (Figure 1).
OS since time of dRT to metastatic site by histology. Patients with poorly differentiated histology had a median OS of 33.6 years (95% CI, 1.7–5.5 years), which was significantly lower than the median OS of 8.5 years (95% CI, 5.6–11.5) for those with differentiated tumors (log-rank P=.003).
Abbreviations: dRT, definitive radiotherapy; OS, overall survival; RT, radiotherapy.
Citation: Journal of the National Comprehensive Cancer Network 23, 1; 10.6004/jnccn.2024.7072
Progression-Free Survival
Median PFS following first dRT was 17 months (95% CI, 10–24 months), with 1-, 2-, and 3-year estimates of 65% (SE, 5%), 44% (SE, 5%), and 23% (SE, 5%), respectively. PDTC histology was again associated with worse PFS outcomes (HR, 2.20; 95% CI, 1.24–3.90;]; P=.007), with a median PFS of 8 months (95% CI, 1–17 months) and 1-year PFS of 50% (SE, 12%) versus 21 months (95% CI, 13–29 months) and 68% (SE, 5%), respectively, for differentiated histologies. On univariate analysis, thoracic site (HR, 0.60; 95% CI, 0.39–0.91; P=.017) was associated with improved PFS, whereas bone site was associated with worse PFS (HR, 1.59;0 95% CI, 1.02–2.47; P=.039); however, on multivariable analysis only histology remained significant. No other disease characteristics or systemic disease status variables were associated with PFS (Supplementary Table S3).
Patterns of Progression
Following the 207 dRT courses, there were 154 subsequent episodes of disease progression with 17 incidents of progression at previously irradiated sites (in-field), representing a 5% crude local failure rate per site and 8% per treatment course. Only 7 of the 17 sites represented isolated sites of local failure without other evidence of distant progression, suggesting the most common site of next recurrence was almost always a new distant site. The actuarial local control rates at 1 year, 2 years, 3 years, and 5 years were 97% (SE, ±1), 94% (SE, ±2), 91% (SE, ±3%), and 86% (SE, ±4%), respectively.
RT-Related Toxicities
Overall dTR toxicity rates were low, with 23 grade ≥2 toxicities related to RT (Table 2). These toxicities occurred during 18 dRT courses among 16 patients, occurring at a median of 1.5 months (range, 0.5–27.3 months) after RT delivery, with 89% observed within 6 months. Three grade 3 events (pneumonitis requiring hospital admission with supplemental oxygen, esophagitis requiring hospitalization for dehydration and failure to thrive, and esophageal stenosis requiring serial dilations) occurred in 3 separate patients at a rate of 1.5% across courses and 2.5% per patient. There were no grade 4–5 events directly attributable to dRT.
CTCAE Grade 2 or 3 Toxicities
| CTCAE Category | Grade 2 (n=20) |
Grade 3 (n=3) |
|---|---|---|
| Pneumonitis | 6 | 1 |
| Esophagitis | 4 | 1 |
| Esophageal stenosis | 0 | 1 |
| Nausea | 2 | 0 |
| Fatigue | 1 | 0 |
| Dysphagia | 2 | 0 |
| Dysarthria | 1 | 0 |
| Dermatitis | 1 | 0 |
| Chest wall pain | 2 | 0 |
| Dysgeusia | 1 | 0 |
Time to Progression
After each dRT (n=207), time to progression (TTP) was a median of 12.6 months (95% CI, 10.8–14.5 months). Shorter TTP following dRT was associated with PDTC histology (P<.001), subsequent dRTs (P<.001), greater number of sites treated per dRT (P=.005), nonthoracic location (P<.001), and osseous site (P=.003). There were no associations with the presence of ongoing systemic therapy (P=.22) or planned continuation of systemic therapy (P=.135).
PDTC and oncocytic histologies had significantly worse outcomes, with median TTP of 6.2 and 8.5 months, respectively, compared with follicular and papillary, at 18.1 and 15.3 months, respectively (Supplementary Table S4). TTP also varied significantly by anatomic site treated per dRT course (log-rank P<.001), with thoracic treatment sites associated with significantly longer TTP (Figure 2B). The thoracic site TTP was 18.6 months, whereas other sites had lower TTP (Supplementary Table S4). Additionally, TTP varied by the number of target sites per treatment course (log-rank P=.018). No significant difference was observed in TTP when treating a single site (13.2 months; 95% CI, 10–16.4 months) versus 2 separate lesions (14.7 months; 95% CI, 11–18 months); however, a shorter TTP was associated with courses for 3 to 5 targets (7.5 months; 95% CI, 4–11 months) (Figure 2C).
TTP and systemic therapy escalation. Several variables were associated with unfavorable or favorable TTP, including (A) poorly differentiated histology with shorter TTP compared with DTCs, (B) thoracic metastasesa with longer TTP, and (C) shorter TTP with 3–5 treated lesions or (D) subsequent dRT courses. (E) Systemic therapies before radiation (pre-RT) and after completing radiation (post-RT) were recorded for each patient to identify systemic therapy escalation subsequent to dRT. (F) Patients with oligometastatic disease had a significant increase in longer time to systemic therapy escalation than those with oligoprogressive disease. For patients with oligometastatic disease, the median time to systemic therapy escalation was 95 months (95% CI, 17–173 months) versus 29 months (95% CI, 26–32 months) for patients with oligoprogressive disease (P=.001).
Abbreviations: Chemo, chemotherapy; dRT, definitive radiotherapy; DTC, differentiated thyroid cancer; ICI, immune checkpoint inhibitor; KI, kinase inhibitor; RT, radiotherapy; TTP, time to progression.
aMultiorgan (n=10) and head and neck courses (n=4) were excluded for analysis.
Citation: Journal of the National Comprehensive Cancer Network 23, 1; 10.6004/jnccn.2024.7072
The last variable found to correlate with TTP was the number of dRT courses. Subsequent dRT courses had shorter TTP (log-rank P<.001), with a first-course TTP of 18 months (95% CI, 10.5–26 months), second-course TTP of 8.5 months (95% CI, 2–15 months), and third-course or greater TTP of 6.2 months (95% CI, 3.5–9 months) (Figure 2D).
Time to Systemic Therapy Escalation
Following the first dRT, the median time to systemic therapy escalation was 4.1 years (95% CI, 1.7–6.5 years). At 2 years, systemic therapy escalation was deferred for 73% (SE, 4%) of living patients, and at 5 years, escalation was still deferred for 46% (SE, 6%). On univariate analyses, the only factor associated with longer deferral to systemic therapy escalation was oligometastatic (vs oligoprogressive) disease (HR, 3.2; 95% CI, 1.6–6.5; P=.001), whereas shorter intervals to next-line systemic regimens were seen for PDTC histology (HR, 2.2; 95% CI, 1.1–4.5; P=.031) and prior receipt of systemic therapy before dRT (HR, 1.9; 95% CI, 1.0–3.6; P=.040). On multivariable analysis, only oligometastatic disease (HR, 0.25; 95% CI, 0.12–0.52; P<.001) and greater total number of sites treated since presentation (≥3 vs 1–2) (HR, 2.07; 95% CI, 1.16–3.71; P=.014) were associated with time to systemic therapy escalation. There were no associations between time to systemic therapy escalation and prior RAI, number of courses, or ongoing systemic therapy (Supplementary Table S5).
Systemic therapies before and after dRT were recorded to identify post-RT systemic therapy escalation. Most patients did not have escalation of their systemic therapy after dRT despite oligometastatic or oligoprogressive disease unless they were not currently receiving systemic therapy (Figure 2E). At 2, 3, and 5 years, the proportions of patients alive without starting a next-line regimen for oligometastatic versus oligoprogressive disease were 92% (SE, 4%) versus 64% (SE, 6%), 90% (SE, 5%) versus 39% (SE, 7%), and 62% (SE, 11%) versus 36% (SE, 7%), respectively (Figure 2F).
Systemic Therapy Details
At initial dRT, most patients (n=92; 77%) were not receiving systemic therapy. Regimens for the remaining 27 (6 of whom were receiving second-line therapy) included KI monotherapy (n=10) or combination therapy (n=5), immunotherapy (n=8), or a combination of both (n=4).
Following RT, systemic therapy was deferred for 90 patients (including 2 planned cessations), whereas 24 maintained the same regimen and 5 switched to a new KI. For the 24 who continued the same therapy, such regimens consisted of KI monotherapy/combination therapy (n=10/n=3), immunotherapy (anti–PD-1/PD-L1 [n=1]; anti–CTLA-4 [n=5]; dual immunotherapy [n=1]), or combination KI plus immunotherapy (n=4). Among the 344 dRT cases, 146 courses had no planned systemic therapy following RT (including 3 holidays/cessations of ongoing therapies), serving as a deferral strategy.
After the first dRT, 43 (36%) patients had systemic therapy escalation following disease progression, including addition of KI monotherapy (n=29) and combination therapy (n=13), immunotherapy (n=5), or a combination of both (n=3). However, by their last follow-up, 43 (51%) of the 84 living patients were on active surveillance without systemic therapy.
Somatic Alterations
Somatic testing was performed in 103 (87%) patients. Among the 103 samples submitted to molecular testing, 95 (92%) were tested with NGS panels, 4 (4%) with BRAF V600E immunohistochemistry, and 4 (4%) with BRAF/RAS DNA sequencing. Oncogenic drivers were identified in 80 (78%) of the cases, and the oncogenic drivers were mutually exclusive except for one tumor harboring both an NRAS and a KRAS mutation (Figure 3). Drivers were strongly associated with histologic diagnosis (Fisher exact P<.001). Late genomic events, typically seen in aggressive disease, were observed in a high proportion of cases, including 42% of TERT promoter mutations and 11% of TP53 mutations (Figure 3). No significant associations were observed with p53 or TERT promoter mutations with respect to study outcomes (OS, PFS, TTP, systemic therapy escalation). However, RAS mutation was associated with shortened TTP (HR, 1.4; 95% CI, 1.0–2.0; P=.04), whereas BRAF mutation was associated with improved PFS (HR, 0.59; 95% CI, 0.37–0.95; P=.029). Median PFS for patients with BRAF mutations was 24.5 months (95% CI, 12.2–36.8 months) versus 14 months (95% CI, 10.7–17.2 months) for patients with wild-type tumors (log-rank P=.027). This BRAF association remained significant (HR, 0.56–0.60; P=.018–.033) on separate multivariable analyses accounting for prior systemic therapy (HR, 1.66; P=.074), ongoing systemic therapy (HR, 1.07; P=.793), and planned initiation of systemic therapy thereafter (HR, 1.07; P=.794).
Genomics from patients with differentiated thyroid cancer.
Abbreviations: FTC, follicular thyroid cancer; OC, oncocytic thyroid cancer; PDTC, poorly differentiated thyroid cancer; PTC, papillary thyroid cancer.
Citation: Journal of the National Comprehensive Cancer Network 23, 1; 10.6004/jnccn.2024.7072
Discussion
Results reported in this retrospective study support the use of dRT for oligometastatic and oligoprogressive thyroid cancer, given that there was excellent local control and tolerability as well as prolonged time observed for escalation of systemic therapy (median, 4.2 years) compared with historical data (median, 1.2 years).22 At the time of first or second progression after initial RT, numerous patients received additional local treatment, with the goal of prolonging time to systemic therapy escalation. For low-volume or slow-growing metastatic DTC, the ability to defer escalations in systemic therapy (and their associated toxicities) can have a significant impact on patients’ quality of life given the adverse effect risks and financial burden associated with lifelong daily-maintenance systemic therapy. Analyses have shown that patients with RAIR DTC treated with lenvatinib who have a lower baseline tumor burden have prolonged OS compared with patients with high tumor burdens.23 This highlights a potential role of dRT in decreasing systemic tumor burden before initiating lenvatinib to assist in prolonging OS.
Current guidelines support RT for palliation of progressive or symptomatic metastases in RAIR DTC, but do not explicitly advocate for dRT, likely due to a paucity of strong evidence on the efficacy of RT in the oligometastatic or oligoprogressive setting.21,24,25 To our knowledge, there has been only one systematic review of patients treated with stereotactic radiotherapy for metastatic DTC, wherein 146 patients with 267 lesions were identified across small and heterogeneous retrospective series.26 These patients had excellent 1-year local control of 82%, median disease-free survival of 12 months, 3-year cancer-specific survival of 72%, and no grade 3–5 toxicities.26 Individually, however, the current literature comprises single-case reports or small series focusing on treatment to specific anatomic sites.27,28
Our analysis constitutes the largest institutional series with consistent practice patterns among providers and longer follow-up, emphasizing that dRT can impart excellent control rates with minimal toxicities for oligometastatic and oligoprogressive thyroid cancer. Limitations of our work include the retrospective nature, lack of a direct comparison cohort who received systemic therapy alone, and heterogeneity in patient presentations, with worse outcomes consistently noted among patients with poorly differentiated histologies (suggesting better systemic therapies are needed for this more aggressive subtype). Additionally, there was minimal representation of a few anatomic sites in our cohort, such as brain and abdominopelvic locations (eg, liver), likely because these metastatic sites often correlate with more advanced and widespread polymetastatic disease (and thus such patients were excluded from analysis).29,30 Furthermore, the limited follow-up period may have hindered our ability to observe late RT-associated toxicities and to definitively interpret outcomes at longer time intervals post-RT. Clinical trials are warranted to evaluate the benefit of dRT and other local modalities (metastasectomy, radiofrequency ablation, cryoablation, and embolization) in the setting of oligometastatic and oligoprogressive thyroid cancer.31
Conclusions
Our results suggest that sequential dRT courses for oligometastatic and oligoprogressive thyroid cancer are a feasible strategy for durable local control and are safe to deliver repeatedly for multiple distant sites. This suggests the potential for dRT to be used as a strategy for deferring systemic therapy escalation and/or providing treatment breaks from chemotherapy. Prospective trials are warranted to formally validate this concept and elucidate the full benefit of dRT in enhancing outcomes as part of a multidisciplinary approach for metastatic thyroid cancer.
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