Rare case of life-threatening thrombocytopenia occurring after radiotherapy in a patient treated with immune checkpoint inhibitor.

Immune checkpoint inhibitors (ICIs) improve significantly outcome of patients with advanced renal cancer. Although immune-related adverse events involve frequently skin, digestive tract, lung, liver and endocrine organs, haematological toxicities are rare. We describe the case of a patient with metastatic renal cancer who was treated with nivolumab. Eight courses of nivolumab were administered without any toxicity; brain metastases were then diagnosed and treated with stereotactic radiotherapy. As the extra-cranial disease was stable, the ninth course of nivolumab was administered 5 days after the end of radiotherapy. One week later, he presented with rectal and nasal bleeding in a context of severe thrombocytopenia (1000/mm). High dose of steroids and intravenous immunoglobulin reversed slowly the thrombocytopenia. This case highlights the possibility of life-threatening thrombocytopenia with ICIs. Interestingly, the close time relation with radiotherapy highlights a potential interaction, warranting a close follow-up of patients in this situation.