Nivolumab is a humanized IgG4 and programmed death 1 (PD-1) monoclonal antibody that has demonstrated antitumor efficacy in clinical trials of various malignant tumors including non-small-cell lung cancer and head and neck squamous cell carcinoma (SCC). However, patients with multiple primary malignancies were excluded in clinical trials. Thus, the efficacy of nivolumab in such patients has not been revealed yet. The programmed death ligand 1 (PD-L1) expression level is currently the main predictive biomarker of PD-1 inhibitors in various types of solid tumors and hematological malignancies. Here we describe a patient with synchronous double primary carcinomas of hypopharyngeal SCC and lung adenocarcinoma who exhibited different responses to nivolumab. After nivolumab treatment, hypopharyngeal SCC with moderate PD-L1 positivity by immunohistochemical staining showed a remarkable response; conversely, nivolumab was not effective against lung adenocarcinoma, which was negative for PD-L1. This suggests that tumors with different PD-L1 expressions may exhibit different responses to PD-1 inhibitors when multiple primary malignancies are present within one patient.
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