Cycle-dependent eosinophilia due to adjuvant nivolumab for malignant melanoma

Immune checkpoint inhibitors (ICIs) have been widely used in the contemporary anticancer armamentarium. However, new side effects due to these agents have continued to emerge.

We describe herein a 71-year-old patient who received nivolumab as adjuvant therapy for malignant melanoma of the skin. He developed eosinophilia starting at 4 weeks of therapy. Eosinophilia increased progressively during the first six nivolumab cycles, then stabilized. Cycle-dependent increments were observed. Subsequently, the patient experienced well-known side effects of ICIs such as grade 1 diarrhea, arthralgias, and erythematous papular rash.

Nivolumab was continued, and absolute eosinophil counts were monitored. Prednisone 10 mg PO daily was required for moderate gastroenteritis, dermatitis, and arthritis, which all subsequently improved. Eosinophil levels gradually downtrended after starting prednisone. Causality assessment between nivolumab and eosinophilia via adverse drug reaction (ADR) probability scale revealed a score of 9.

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.