Merkel-Cell Carcinoma: Local Recurrence Rate Versus Radiation Dose Study from a 949-Patient Database

(1) Background: Knowledge regarding the optimal radiotherapy dose for Merkel-cell carcinoma (MCC) remains limited. (2) Methods: Following a PubMed search, equivalent doses in 2 Gy fractions (Gy2) were compared. (3) Results: Of the 949 patients, 939 were evaluable, with 728 (77.5%) cases localized to the primary site and 171 irradiated without chemotherapy. The overall local recurrence rate (LRR) was 23% (40/171). After definitive radiotherapy with EQD2 < 50 Gy2 versus ≥50 Gy2, the LRRs were 23.1% (3/13) and 12.5% a(1/8), respectively (p = 0.0004). (4) Conclusions: For definitive radiotherapy, EQD2 < 50 Gy2 demonstrates a significantly higher LRR than ≥50 Gy2 (p = 0.0004). This study is clinically useful and unique with stratification by definitive/adjuvant settings and positive/negative resection margins. A future prospective multicenter study is needed to determine the optimal radiotherapy doses.