A case of primary malignant melanoma of the lung responded to anti-PD-1 antibody therapy

Primary malignant melanoma of the lung (PMML) is an exceedingly rare type of melanoma. Here, we report a case of an 86-year-old Japanese woman who was diagnosed as PMML with subcarinal lymph node metastasis. She was treated with intravenous administration of programmed cell death-1 (PD-1) inhibitor, nivolumab. After the treatment, lymph node lesion regressed. The size of primary lesion was also controlled in combination with radiotherapy. In this case, two histological features were noted in the biopsy specimen that supported a response to nivolumab: membranous expression of programmed death ligand-1 (PD-L1) in tumor cells and dense scattered infiltration of CD8+ TILs. The clinical course of this case suggests that certain PMML cases may also respond to anti-PD-1 therapy.