Radiotherapy for cutaneous malignant melanoma: rationale and indications.

The use of radiation as adjuvant therapy for patients with cutaneous malignant melanoma has been hindered by the unsubstantiated belief that melanoma cells are radioresistant. An abundance of literature has now demonstrated that locoregional relapse of melanoma is common after surgery alone when certain clinicopathologic features are present. Features associated with a high risk of primary tumor recurrence include desmoplastic subtype, positive microscopic margins, recurrent disease, and thick primary lesions with ulceration or statellitosis. Features associated with a high risk of nodal relapse include extracapsular extension, involvement of four or more lymph nodes, lymph nodes measuring at least 3 cm, cervical lymph node location, and recurrent disease. Numerous studies support the efficacy of adjuvant irradiation in these clinical situations. Although data in the literature remain sparse, evidence also indicates that elective irradiation is effective in eradicating subclinical nodal metastases after removal of the primary melanoma. Consequently, there may be an opportunity to integrate radiotherapy into the multimodality treatment of patients at high risk of subclinical nodal disease, particularly those with an involved sentinel lymph node. Such patients are known to have a low rate of additional lymph node involvement, and thus in this group, a short course of radiotherapy may be an adequate substitute for regional lymph node dissection. This will be the topic of future research.