Objective: To review the therapeutic strategy in Merkel cell carcinoma (MCC) treated with radiotherapy (RT) discussed in a multidisciplinary tumour board. Methods: Clinical records of patients with a diagnosis of MCC and with an indication to undergo RT at the European Institute of Oncology between 2003 and 2018 were reviewed retrospectively. Results: Twenty-six patients were included in the analysis (median age 65 years, range 42–87). Nineteen received adjuvant RT, 4 exclusive RT, and the remainder palliative RT. Intensity-modulated RT was used in 13 cases, a 3D conformal technique in 11 cases, and stereotactic RT in 2 cases. No major toxicities were recorded. The median relapse-free survival (RFS) after adjuvant RT was 20.5 months, while for unknown primary MCC, it was 23 months. In the adjuvant setting, median polyomavirus-positive RFS was 21.5 months (range 1–49) and median polyomavirus-negative RFS was only 14 months (range 4–45). Overall, RFS of polyomavirus-positive and polyomavirus-negative patients was 10.5 and 8 months, respectively. After adjuvant RT, only 1 out of 10 patients had a recurrence in the RT field. At the time of data collection, 16 patients were alive with no evidence of disease, 1 patient was alive with advanced status of disease, 8 patients died of disease progression, and 1 patient died of other causes. Conclusions: The management of unknown primary and polyomavirus-positive cases, which had a better prognosis in our series, may benefit from a multidisciplinary approach, given the limited data available regarding optimal treatment.
Merkel cell carcinoma of lymph node with unknown primary has a significantly lower association with Merkel cell polyomavirus than its cutaneous counterpart