Acute skin reaction suggestive of pembrolizumab-induced radiosensitization.

The combination of localized radiotherapy and immune checkpoint inhibitors represents a promising therapeutic strategy for various cancers, including metastatic melanoma. Radiation therapy may enhance tumor antigen presentation and cytokine release, which may optimize the systemic antitumor immune response induced by these immunotherapeutic antibodies, with a potential delayed abscopal effect. However, clinical experience of using immune checkpoint inhibitors with concurrent radiotherapy remains scarce. We report here for the first time a case suggestive of acute skin radiosensitization induced by pembrolizumab, with a suggestive time relationship between the completion of ionizing radiation, drug administration, and rapid onset of the skin reaction. This suggests that radiation therapy may also interact rapidly with anti-programmed-death 1 antibodies. Therefore, caution should be exercised when prescribing this combination therapy in advanced cancers.