Post operative single fraction radiation therapy in Merkel cell carcinoma of the head and neck

Cook, Maclean M.; Schaub, Stephanie K.; Goff, Peter H.; Fu, Alex; Park, Song Y.; Hippe, Daniel S.; Liao, Jay J.; Apisarnthanarax, Smith; Bhatia, Shailender; Tseng, Yolanda D.; Nghiem, Paul T.; Parvathaneni, Upendra

PURPOSE: Conventionally fractionated, post-operative radiotherapy (cPORT; 50 Gy in 25 fractions) is considered for patients with Merkel cell carcinoma (MCC) to improve locoregional control. However, cPORT is associated with acute toxicity, especially in the head and neck (H&N) region, and requires daily treatments over several weeks. We previously reported high rates of durable local control with minimal toxicity using 8 Gy single-fraction radiation therapy (SFRT) in the metastatic setting. We report early results on a cohort of patients with localized H&N MCC, who received post operative SFRT if a cPORT regimen was not feasible. METHODS: Twelve patients with localized MCC of the H&N (clinical/pathologic stages: I-II) and no prior RT to the region were identified from an IRB-approved prospective registry who underwent surgical resection followed by post operative SFRT. Time-to-event was calculated starting from the date of resection prior to SFRT. The cumulative incidence of in-field locoregional recurrences and out-of-field recurrences was estimated with death as a competing risk. RESULTS: Twelve H&N MCC patients were identified with clinical/pathologic stages I-II H&N MCC. Median age at diagnosis was 81 years (58-96); 25% had immunosuppression. At a median follow-up of 19 months (range: 8-34), there were no in-field locoregional recurrences. A single out-of-field regional recurrence was observed, which was successfully salvaged. There were no MCC specific-deaths. No radiation-associated toxicities greater than grade 1 (CTCAE v5) were observed. CONCLUSIONS: Preliminary data suggest that SFRT could offer a potential alternative to cPORT to treat the primary site for localized H&N MCC, particularly in elderly or frail patients, with promising in-field local control and minimal toxicity. Further data with validation in larger cohorts is needed to confirm the sustained safety and efficacy of post operative SFRT.