Cycle-dependent eosinophilia due to adjuvant nivolumab for malignant melanoma.

Physicians and pharmacists need to be aware of this important side effect of ICI therapy. Eosinophilia in the context of ICI use has been previously reported in clinical trials. Our case is unique as eosinophilia was cumulative, showed increments every 8 weeks, and exhibited a trend toward cycle dependency. Extensive and expensive workup does not appear warranted, and simple monitoring of complete blood count is appropriate in most patients. Further studies are necessary to assess the true incidence, pattern, and severity of eosinophilia related to ICIs as well as its association with clinical outcomes.