Eosinophilic, polymorphic, and pruritic eruption associated with radiation therapy in two patients diagnosed with prostate cancer.

Key Clinical Message: We report 2 cases of EPPER diagnosed in patients who received radiation therapy and hormonal therapy for locally advanced prostate cancer. Both our patients developed this rare late toxicity, but early diagnosis and treatment of this adverse event offers a good prognosis, with no unnecessary interruptions of oncological treatment required. Abstract: Acute and late adverse events are a major problem for patients receiving radiation therapy. We describe two cases of eosinophilic, polymorphic, and pruritic eruption associated with radiotherapy (EPPER) syndrome, a very uncommon toxicity that affects cancer patients. Both our cases were men diagnosed with localized prostate cancer and were treated with radiotherapy and hormonal therapy. They developed EPPER during and after completing the total radiation dose. Multiple tests and skin biopsies were performed in order to find a superficial perivascular lymphohistiocytic infiltrate, confirming EPPER. The patients received corticotherapy and fully recovered after this treatment. There are a few more cases of EPPER reported in the literature, but the pathogenic mechanism is still unknown. EPPER is an important side effect of radiation therapy and it is probably underdiagnosed, due to its occurrence (usually after completing the oncological treatment).