Unexpected pure red series aplastic anemia secondary to pembrolizumab treatment: a case report and literature review.

Pembrolizumab is a treatment that has shown a survival benefit in patients with metastatic melanoma. Programmed death receptor 1 inhibitors are new therapeutic agents that produce clinical responses with a more manageable profile of adverse effects compared to chemotherapy. The most frequent adverse effects include fatigue, rash, myalgia, pyrexia and cough, with less frequent occurrence of immune-mediated adverse reactions such as colitis, pneumonitis, hepatitis and encephalitis. Immune-related hematological toxicities have been poorly described. Here we present the case of a patient with metastatic melanoma who develops pure red series aplasia after almost 3 years of treatment with pembrolizumab. To our knowledge, this is the first case of aplastic anemia during treatment with pembrolizumab, with some peculiarities compared to the published cases in the literature.