Initial asymptomatic grade 3 neutropenia converted into febrile grade 3 neutropenia on day 32 after the first dose of nivolumab, improved with stopping ICI and concurrent treatment with G-CSF. However, on day 77, the patient had to be retreated with G-CSF as neutrophil count became 500/mL, which normalized immediately after the treatment. The gene discussed is CSF3; the disease is neutropenia.