Hypercalcaemia due to Sarcoidosis during Treatment with Avelumab for Metastatic Merkel Cell Carcinoma

Merkel cell carcinoma is a rare but aggressive skin cancer. Response to chemotherapy is not durable but avelumab, an anti-PD-L1 inhibitor, showed promising ongoing response in a phase II trial. Checkpoint inhibitors including avelumab are known to cause overactivation of the immune system, leading to immune-related adverse events (irAE). We describe the first reported case of hypercalcaemia secondary to reactivation of sarcoidosis in a patient with metastatic Merkel cell carcinoma on avelumab. Hypercalcaemia was managed with corticosteroids to full resolution and avelumab therapy was safely continued.