Multiple Phenotypic Conversion in Malignant Melanoma: Obtainment of Granulocyte Colony-Stimulating Factor-Producing Ability during the Intermission of Nivolumab Therapy

Malignant melanoma (MM) is one of the most aggressive, recalcitrant, and recurrence-prone skin neoplasms. Its feature is likely to be associated with phenotypic conversion due to tumor heterogeneity. The multidisciplinary assessment, including surgery, drug therapy using anticancer agents and immune checkpoint inhibitors, and radiotherapy, is needed for the treatment of advanced MM. Herein, we report a long-term follow-up MM, in which multiple phenotypic conversion occurred during several treatments. In particular, our case obtained granulocyte colony-stimulating factor-producing ability during the intermission of nivolumab therapy and it was successfully controlled by re-administration of nivolumab. Sharing the case having a varied clinical course is meaningful to increase the knowledge and decision branches for the treatment of melanoma.