Definitive radiotherapy or chemoradiotherapy in the treatment of Merkel cell carcinoma.

Merkel cell carcinoma (MCC) is a radiosensitive tumour. Radiotherapy has an important role in its treatment, including definitive management. This study aimed to determine the in-field control achieved with definitive radiotherapy or chemoradiotherapy (CRT) and to examine patterns of relapse.Patients treated with definitive radiotherapy or CRT for biopsy-confirmed MCC were identified from records of the Royal Prince Alfred Hospital and Melanoma Institute Australia. Definitive treatment was defined as treatment delivered to macroscopic or residual microscopic disease at the primary site or in regional nodes. Patients with distant metastatic disease at presentation and those treated electively or adjuvantly (i.e. after microscopically clear excision) were excluded.Of 26 patients treated with definitive radiotherapy (n = 18) or CRT (n = 8), 20 were disease free at last follow-up (median follow-up 23.5 months). Five of the six patients who recurred did so at distant sites, with two experiencing simultaneous in-field failure at treated nodal sites where there had been macroscopic disease at presentation. Eighty-nine per cent of all patients and 85% of those with macroscopic disease were free of in-field recurrence at 2 years.Definitive radiotherapy or CRT produces excellent in-field disease control in the treatment of primary and regionally metastatic MCC.