Characterization of clinical outcomes after shorter course hypofractionated and standard-course radiotherapy for stage I-III curatively-treated Merkel cell carcinoma

•Efficacy of hypofractionated radiotherapy for Stage I-III Merkel cell carcinoma is not well-described.•There was no difference in cumulative incidence of in-field locoregional relapse or MCC-specific survival between hypofractionated and conventionally-fractionated radiotherapy.•On multivariable analysis, immunosuppression, clinical stage III disease, and lymphovascular invasion were associated with any recurrence when controlling for sex, age, and hypo-RT. Limited data exists regarding the efficacy of curative hypofractionated radiotherapy (hypo-RT) regimens compared to conventionally-fractionated radiotherapy (conv-RT) for Merkel cell carcinoma (MCC). A retrospective analysis of 241 patients diagnosed with non-metastatic MCC from 2005-2021 and who received RT at Dana-Farber/Brigham & Women’s Cancer Center. The primary outcome was cumulative incidence of in-field locoregional relapse using Gray’s test with competing risks of death and isolated out-of-field recurrence. Secondary outcomes included overall survival (OS) and MCC-specific survival using log-rank tests, and risk factors of recurrence using Cox-proportional hazards regression. There were 50 (20.6 %) and 193 (79.4 %) courses of hypo-RT and conv-RT, respectively. The hypo-RT cohort was older (≥73 years at diagnosis: 78.0 % vs 41.5 %, p