Post-operative radiation therapy in patients with early-stage merkel cell carcinoma: Analyses from an institutional cohort and national data set

Summary: Abstract Body: Introduction: Merkel cell carcinoma (MCC) is an aggressive skin cancer. Postoperative radiation therapy (PORT) is employed in the management of stage I-II MCC, especially cases with high-risk features: head and neck site, tumor >1cm, immunosuppression, and lymphovascular invasion present. This study aims to characterize early-stage patients who received PORT and to quantify the effect of PORT on 5-year disease-specific survival (DSS) and recurrence free survival (RFS). Methods: In the institutional cohort (IC), 108 stage I-II MCC patients, diagnosed 2017-2023, were included in demographic and survival analyses. Using SEER, a national cohort (NC) of 2423 stage I-II MCC patients was included in complementary analyses. Results: Patients who received PORT were younger than patients treated with surgery monotherapy (median age 70 years old vs. 75 in the IC, p=0.026; and 72 vs. 77 in the NC, respectively). There were no statistically significant differences between treatment groups in terms of gender, tumor site, or immunosuppression status in the IC. DSS was higher for patients treated with surgery monotherapy (95.6% IC; 87.5% NC - stage I) than those treated with PORT (73.2% IC, p=0.03; 82.8 NC - stage I). RFS tended to be higher for patients treated with surgery monotherapy than PORT (81.1% vs. 68.0% in the IC respectively, stage I, p=0.3). Discussion: The decision to utilize PORT for patients with early-stage MCC requires nuance, and not all stage I-II MCC patients will benefit from PORT. When stage I and II MCC patients were analyzed as single groups, PORT was not associated with improved DSS or local control. It is possible that the use of PORT reflects unmeasured prognostic factors not captured in these datasets, such as postoperative margin status. Regardless, these data suggest that further studies on appropriate use criteria for PORT in early-stage MCC would be helpful. Marcus Curlin¹, Tucker Hansen¹, Anthony J. Apicelli¹, Lynn Cornelius¹, Aubriana M. McEvoy¹ 1. Washington University in St Louis, St. Louis, MO, United States. Clinical Research: Interventional Research