Systemic Antitumor Effects and Abscopal Responses in Melanoma Patients Receiving Radiation Therapy

Background: Malignant melanoma represents the deadliest form of skin cancer with a high tendency to metastasize during the early course of the disease. Radiation therapy has long played a key role in the management of both local and metastatic melanoma. Although local radiation therapy exerts antitumor effects by damaging the cellular DNA, it also induces an important out-of-field (distant) effect known as the "abscopal effect" in nonirradiated sites. Radiation therapy-induced abscopal effects are believed to be mediated by activation and stimulation of the immune system. Objective: To provide a detailed overview of the current state of knowledge and clinical experience of radiation therapy-induced abscopal effects in patients with malignant melanoma. Methods: Using electronic databases such as MEDLINE via PubMed and Google Scholar, a systematic literature review was performed to find published clinical evidence for radiation therapy-induced abscopal effects in patients with malignant melanoma. The clinical data on radiation therapy-induced abscopal effects were reviewed and the outcomes summarized. Results: Clinical evidence of patients with malignant melanoma was gathered using databases from MEDLINE and those findings were summarized. Although the precise mechanism of the abscopal effect of radiation therapy is still not completely understood, evidence suggests that tumor cell destruction by radiation releases tumor antigens that stimulate the immune system of the host to activate the body's immune effector cells systemically and produce distant non-target antitumor effects. This forms a basis for using the radiation therapy with immunotherapy to augment the abscopal response rates. Conclusions: Current clinical evidence suggests that there is a large potential to enhance the abscopal effect when radiation therapy is combined with immunotherapeutic agents for the treatment of malignant melanoma. Ongoing and planned clinical trials may provide us with a more in-depth understanding of how this combination therapy can be optimally utilized clinically to achieve improved survival outcomes among patients with malignant melanoma.