Severe eosinophilia and subsequent dermatologic immune‐related adverse event with squamous cell carcinoma antigen elevation induced by nivolumab and ipilimumab

Immune checkpoint inhibitors (ICIs) for malignant lesions are associated with immune‐related adverse events (irAEs), but reports about severe eosinophilia induced by ICIs are scarce. A 73‐year‐old man with lung squamous cell carcinoma was treated by chemotherapy (carboplatin plus paclitaxel) and ICIs (nivolumab plus ipilimumab). After two cycles of chemotherapy, the ICIs were continued. After 5 months, the eosinophilia, which had exceeded 5000/μl, increasingly deteriorated, and the only detected irAE was a grade 1 rash. Under continuation of the ICIs, although the eosinophilia decreased, a grade 3 rash and severe pruritis subsequently appeared. Squamous cell carcinoma antigen (SCCA) was steeply increased simultaneously. A complete response had been achieved, and oral prednisolone markedly improved the rash, pruritis, and eosinophilia. Clinicians should be aware that precedent severe eosinophilia and subsequent severe irAE could occur in patients treated by nivolumab and ipilimumab, and SCCA elevation could be associated with dermatologic irAE.