Radiation therapy utilization and survival associations in metastatic Merkel cell carcinoma in the immunotherapy era: A national database study.

e21561 Background: Immune checkpoint inhibitors (ICIs) have become the standard first-line systemic therapy for metastatic Merkel cell carcinoma (MCC). Radiotherapy (RT) remains commonly used for local control and palliation, and growing biologic interest suggests that RT may enhance antitumor immune responses when combined with ICIs. However, population-level evidence regarding contemporary patterns of RT use and its association with survival in immunotherapy-treated patients with metastatic MCC is limited. Methods: We conducted a retrospective population-based cohort study using the National Cancer Database (NCDB), including adults diagnosed with metastatic MCC between 2011 and 2022. Temporal trends in treatment utilization were described across the study period. Among patients diagnosed in the immunotherapy era (2017–2022), factors associated with receipt of RT were examined using multivariable logistic regression. To evaluate survival, analyses were restricted to immunotherapy-treated patients, and overall survival was compared between those who received RT and those who did not using propensity score-matched Kaplan-Meier and Cox proportional hazards analyses, with a focus on 2-year overall survival. Results: A total of 1,736 patients with metastatic MCC were included. Following 2017, immunotherapy use increased substantially, while chemotherapy use declined; RT utilization remained relatively stable over time. In multivariable analyses restricted to the immunotherapy era, higher primary tumor stage and lymph node dissection were independently associated with RT receipt. Among immunotherapy-treated patients in the propensity score-matched cohort, RT was not associated with improved 2-year OS (aHR,1.09; 95% CI, 0.84-1.42), and Kaplan-Meier analyses demonstrated no significant survival difference. Conclusions: In the contemporary immunotherapy era, RT continues to be selectively incorporated into the management of metastatic MCC, particularly in patients with greater local or regional disease burden. However, among immunotherapy-treated patients, RT was not associated with improved short-term overall survival at the population level. These findings support a continued role for RT in local disease management while underscoring the need for prospective studies to better define its optimal integration with immunotherapy.