Definitive radiotherapy for Merkel cell carcinoma confers clinically meaningful in-field locoregional control: A review and analysis of the literature.

BACKGROUND: Merkel cell carcinoma (MCC) is an uncommon radiosensitive, neuroendocrine malignancy. Treatment often involves surgery; however, older, sicker patients may not be candidates for an operation. Institutions have published data favoring the role of definitive radiotherapy for macroscopic locoregional disease. OBJECTIVE: Our objective was to report the outcome of patients treated with definitive radiotherapy. METHODS: We performed a systematic review of Medline, PubMed, and Embase databases for reported cases or series of definitive radiotherapy for macroscopic locoregional MCC. RESULTS: The mean radiation dose did not significantly differ between primary and regional sites (48.7 ± 13.2 vs 49.4 ± 10.1 Gy, P = .74). The rate of recurrence was calculated on the basis of the site of disease (11.7%) and per patient (14.3%). Recurrence was significantly more likely to occur at regional than at primary irradiated sites (16.3% vs 7.6%, P = .02). There was no association between radiotherapy dose and incidence of recurrence or nonrecurrence; primary (42.7 ± 23 vs 49.3 ± 11.8 Gy, P = .197) and regional (48.6 ± 10 vs 49.5 ± 10.3 Gy, P = .77). LIMITATIONS: A limitation of this report is that most publications were retrospective; heterogeneity was present in the size of MCC and in radiotherapy details. CONCLUSIONS: Definitive radiotherapy for locoregional macroscopic MCC was found to confer clinically meaningful local and regional in-field control.