There is a paucity of evidence on treating patients with Merkel cell carcinoma with definitive radiotherapy. Surgery followed by adjuvant radiotherapy remains the standard of care for most patients with Merkel cell carcinoma. However, the majority of lesions present in the head and neck, and resection is often contra-indicated because of the proximity of nearby structures and the inability to achieve adequate excision margins without compromising form or function. In this group of patients, definitive radiotherapy has been shown by small institution studiesrr to provide similar locoregional control rates as surgery plus adjuvant radiotherapy.
The study by Veness et alr of 43 patients with Merkel cell carcinoma, included patients receiving radiotherapy alone at initial diagnosis (56%) and in the relapse setting (44%). The reported in-field control rate was 75%, and overall survival at 2 and 5 years was 58% and 37% respectively. The median relapse free survival (RFS) was significantly better for patients without nodal metastases present at the time of treatment (38.1 months vs 10.7 months).
The dose response of MCC to radiation has been documented by Footer in 112 patients treated with curative intent. These data suggest that surgical margins do not greatly effect locoregional control if doses greater than 50Gy are used. For microscopic disease, doses of 50Gy are effective and for gross disease doses > 55Gy should be considered. This is illustrated in the table below.
© Int J Radiat Oncol Biol Physicsr
Management of draining lymph nodes is an essential component of treatment. There is level 2 evidence to show that elective nodal radiotherapy improves regional control rates. Sentinel lymph node biopsy/mapping may be useful to guide either elective lymph node dissection or delineation of radiotherapy fields and provides prognostic information. Patients with positive SNLB require nodal treatment. False negative SNLB may occur in up to 20% of cases.r
Based on this, and the proclivity of Merkel cell carcinoma to spread via dermal lymphatics to locoregional nodes, we recommend that radiotherapy fields encompass the primary with a wide-field, in transit lymphatics and the first echelon of draining lymph nodes.
Concurrent chemotherapy remains an active area of investigation, with early studies suggesting high locoregional control rates.