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.