Palliative treatment for in-transit cutaneous metastases of Merkel cell carcinoma using surface-mold computer-optimized high-dose-rate brachytherapy.

Purpose: The objective of this study was to evaluate the palliative treatment benefit of surface-mold computer-optimized high-dose-rate brachytherapy (SMBT) for in-transit cutaneous metastases of Merkel cell carcinoma (MCC).

Methods: Ten patients with in-transit cutaneous MCC metastases were treated with SMBT at the Dana-Farber/Brigham & Women's Cancer Center between 2006 and 2012.

Results: The median age at diagnosis was 76 years (range, 63-87 years). Seven patients had in-transit metastases on the lower extremities (70%), 2 patients on the head and neck (20%), and 1 patient on an upper extremity (10%). A total of 152 metastatic MCC lesions were treated with SMBT. All SMBT-treated lesions resolved clinically within a few weeks of therapy. The median follow-up was 34 months (range, 22-85 months). Two of 152 treated lesions recurred during the study period for a local control rate of 99%. Eight patients (80%) developed additional in-transit metastases outside the original SMBT fields. Five of these 8 patients underwent additional SMBT. At study conclusion, 3 patients (30%) are alive without disease, 3 patients (30%) are alive with disease, and 4 patients (40%) died of MCC.

Discussion: Surface-mold computer-optimized high-dose-rate brachytherapy offers effective and durable palliation for cutaneous metastases of MCC, although it does not appear to alter disease course.