ROS1‑rearranged high‑PD‑L1‑expressing lung adenocarcinoma manifesting as mediastinal tumor: A case report

ROS proto-oncogene 1 receptor tyrosine kinase (ROS1)-rearranged lung cancer is rare and comprises only 1% of lung adenocarcinoma cases. It has recently been reported to have good response to crizotinib, a tyrosine kinase inhibitor of anaplastic lymphoma kinase. Driver oncogene mutations with approved therapies seldom coexist with a high expression of Programmed death-ligand 1 (PD-L1). The present case report describes a rare case of ROS1 rearrangement with high-PD-L1-expressing occult lung adenocarcinoma. A 32-year-old woman presented with chest pain and a prolonged cough. Chest computed tomography (CT) revealed a 57×36-mm tumor in the mediastinum, with no tumors detected in other regions. Positron emission tomography (PET)-CT showed a strong fluorodeoxyglucose accumulation in the tumor (SUVmax 13.2). Mediastinal tumor resection was completely resected using a video-assisted thoracic surgery approach. Pathological examination showed the tumor cells were positive for thyroid transcription factor 1, Napsin-A, ROS1, and PD-L1 (tumor proportion score >99%). ROS1 rearrangement was confirmed by fluorescence in situ hybridization. The mediastinal tumor was diagnosed as mediastinal lymph node metastasis of ROS1-rearranged PD-L1 high-expression undifferentiated lung adenocarcinoma (pathological stage 3, TxN2M0). Two months after the operation, the CT scan showed multiple mediastinum lymph nodes metastases with rapid tumor growth. The patient achieved a complete response after three cycles of S-1 plus cisplatin with concurrent radiotherapy 60 Gy/30 Fr.