Efficacy of radiation therapy in the local control of desmoplastic malignant melanoma.

Background: Desmoplastic malignant melanoma (DMM) is a rare variant of malignant melanoma with high local recurrence rate after surgical excision. We performed a retrospective review to address the role of radiation therapy in local control of this tumor.

Methods: Between 1976 and 1997, 44 patients with the pathologic diagnosis of DMM were registered at our tumor registry. Fourteen patients received postoperative RT, and one patient received preoperative RT. Three of the irradiated lesions had gross residual or positive surgical margins. Doses ranged from 44 to 66 Gy.

Results: Sixty-eight percent of DMM lesions occurred in the head and neck region. Forty-eight percent (21 of 44) of patients experienced a local recurrence after initial excision (mean time to recurrence, 12 months). Local failure in head and neck was 46% (14 of 30). Clark level, primary site, and neurotropism did not predict local recurrence; the Clark level predicted distant metastasis. No viable tumor was found in the surgical specimen of the patient who received preoperative RT. None of 15 patients who received adjuvant irradiation had any additional recurrences (mean follow-up, 64.7 months). By contrast, four of seven patients with history of recurrence who did not receive RT had local relapse (p =.005). The incidence of distant metastasis did not reach statistical significance between the irradiated and nonirradiated groups.

Conclusions: The high rate of local recurrence of DMM after surgical resection is dramatically reduced by adjuvant radiation therapy. We recommend adjuvant postoperative radiation therapy as a part of treatment of DMM.