Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer. Conventional post-operative radiotherapy (cPORT), given in 25-30 fractions (2Gy per fraction) over 5-6 weeks, is associated with improved locoregional control but also with skin toxicity, fibrosis, and wound healing issues. We hypothesized that 1-3 fractions of 8Gy hypofractionated PORT (hPORT), may provide adequate control in the majority of patients with significantly diminished toxicity and a less extensive treatment regimen. 17 patients with locoregional MCC were identified from our prospective registry that received hPORT after an informed discussion that included cPORT versus receiving no RT. The in-field recurrence rate (per site treated) was estimated using the Kaplan-Meier method. 12 patients had local and 5 had nodal MCC with a median age of 75 years. Median follow-up was 483 days. Patients received either 8Gy single-fraction RT (n¼15) or 24Gy in 3 daily fractions (n¼2) in the initial (n¼11) or recurrent (n¼6) setting. RT fields (n¼23) encompassed 17 primary tumor beds and 6 regional node beds. The 1-year recurrence rate infield was 5.0% by Kaplan-Meier estimation. During the entire follow-up period, the in-field recurrence rate was 3/23 (13%). Toxicity was limited to localized skin changes (no greater than CTCAE v5 grade 1), typically for 2-3 days. Supporting the concept that hPORT is effective in controlling local MCC, at 6 months after RT, one patient developed two in-transit recurrences outside the hPORT field, but nowhere within the field. These early findings suggest hPORT can be a viable alternative to cPORT with a low rate of in-field recurrence and minimal toxicity that compare favorably with cPORT. We propose further investigation of hPORT, especially in MCC patients with significant co-morbidities and/or high competing risk of distant metastases.
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