Role of Radiation Therapy as Immune Activator in the Era of Modern Immunotherapy for Metastatic Malignant Melanoma

Metastatic melanoma is difficult to treat, and often portends a grim prognosis. For patients with cerebral metastases, the prognosis is even more dire. Systemic immunotherapy and targeted agents are emerging as the mainstay of treatment for metastatic melanoma. Although immunotherapy has been shown to prolong relapse-free survival and long-term control of micrometastatic disease, the response rate is suboptimal, prompting the need to optimize and improve therapy. Accumulating evidence suggests that in addition to effective locoregional control, radiation therapy (RT) may induce immune activation and expansion of T lymphocytes recognizing melanocyte-specific antigens including activated cytotoxic T lymphocytes that can potentially kill melanoma cells. In some cases, RT contributes to the clearance of metastatic disease in distant, nonirradiated regions, a bystander phenomenon called the abscopal effect. Here, we evaluate the potential promise of ablative radiation treatment in the era of modern immunotherapy by presenting a patient with metastatic melanoma who remained disease free for over 3 years after an initial diagnosis of advanced metastatic melanoma with brain, subcutaneous tissue, mesenteric, pelvic, and retroperitoneal involvement. The patient failed initial stereotactic radiosurgery, but responded to whole-brain RT in combination with interleukin-2 immunotherapy. Thus, combination RT with immunotherapy may be synergistic by promoting the release and processing of melanoma antigens that can be presented by dendritic cells. This in turn may augment the response to therapies that center on expansion and/or activation of antitumor T cells.