Radiotherapy and Conservative Surgery in the Locoregional Management of Merkel Cell Carcinoma: The British Columbia Cancer Agency Experience

Merkel cell carcinoma (MCC) is an uncommon aggressive skin malignancy. Published series mainly focus on wide excision, which can be difficult at some sites (e.g., face) and in patients with comorbidities. In British Columbia, an approach of conservative surgery followed by radiotherapy is common. This is a retrospective review of 179 patients treated for MCC with curative intent in British Columbia. Totals of 68, 63, and 37 patients underwent narrow excision of primary, attempted wide excision, and biopsy only, respectively. Adjuvant radiotherapy reduced local recurrence after narrow excision (< 10 mm margin) from 25 to 4.9 % (p = .03) and was effective in the presence of microscopic positive margins. Local recurrence rate was 7.1 % if the margin was > 10 mm irrespective of radiation use. Local RFS was improved by adjuvant radiation therapy (RT) (p = 0.04), and there was a trend to reduced nodal relapse after elective nodal RT (p = .07). Irradiation of macroscopic tumor at 37 primary and 33 nodal sites provided 5-year local and nodal RFS of 90 and 75 %, respectively. The 5-year cancer specific survival was 77 % and was not improved by the use of adjuvant radiotherapy. Local excision plus adjuvant RT is an effective treatment for MCC. Adjuvant radiation should be considered when the excision margin is < 1 cm.