Pembrolizumab plus platinum-based chemotherapy for unfavorable cancer of unknown primary site: Case report.

Abstract Introduction We report a case of sustained complete response in unfavorable cancer of unknown primary site (CUP) successfully treated with chemotherapy combining pembrolizumab, pemetrexed and platinum. Case presentation A 66-year-old man was presented with weight loss and cough for 3 months. Contrast-enhanced computed tomography (CT) confirmed a mass in the superior anterior mediastinum and multiple enlarged mediastinal and axillary lymph nodes. Positron emission tomography-CT (PET-CT) showed abnormal uptake in the corresponding lesions. Histopathological analysis of the left axillary nodule revealed poorly differentiated adenocarcinoma. Immunohistochemistry showed the tumor cells were positive for cytokeratin 7 and thyroid transcription factor-1 and negative for cytokeratin 20. Thus, the patient was diagnosed as poorly differentiated adenocarcinoma of unknown primary, and treated as non-small-cell lung cancer. Additional genetic testing revealed the patient was negative for EGFR, ALK fluorescence in situ hybridization, ROS1, BRAF, and PD-L1 22C3 IHC with Tumor Proportion Score (TPS) was less than 1%. The patient received six cycles of pembrolizumab, platinum, and pemetrexed intravenously. Cisplatin was switched to carboplatin because of cisplatin nephrotoxicity in one course. PET-CT after six cycles showed all lesions disappeared; complete response was considered to have been achieved. Maintenance therapy of pembrolizumab and pemetrexed has been continued for 6 months after the induction therapies to prevent progressive disease. Complete response has been maintained. Discussion Chemotherapy with pembrolizumab, platinum and pemetrexed could be valuable for treating unfavorable CUP. Conclusion Chemotherapy with pembrolizumab, platinum, and pemetrexed helped achieved sustained complete response in a patient with unfavorable CUP.