2-Year survival benefit from immunotherapy for squamous cell cancer with cancer of unknown primary in mediastinum: a case report.

Cancers of unknown primary (CUP) account for 2%-5% of all diagnosed cancers and are always characterized with fast-paced aggression, early metastasis, and unpredictable spread patterns Mediastinum metastasis with unknown primary origin is extremely rare and with a poor prognosis and short survival. There is no literature to refer to for its treatment. Here, we reported a case of squamous cell CUP in the mediastinum. A 50-year-old male patient was admitted after multi-line treatment of low differentiated squamous cell carcinoma in the mediastinum diagnosed 8 months before. In August 2019, the patient went to a local hospital for cough and dyspnea for 2 weeks. Then, he was diagnosed with squamous cell carcinoma of unknown primary origin with multiple lymph nodes metastasis. The patient was featured with programmed cell death-ligand 1 (PD-L1) expression strongly positive in 90% of tumor cells and the combined positive score of 90 and a tumor mutation burden of 1.79 MUts/Mb and microsatellite stable phenotype. The patient was treated with anti-programmed cell death-1 (PD-1) antibodies in combination with chemotherapy and responded to the treatment. The patient showed stable disease to multi-line immunotherapy for more than 7 months and finally got a clinical benefit of 2-year survival benefit. In conclusion, immunotherapy targeting PD-1/PD-L1 in combination with chemotherapy may play a crucial role in the later-line treatment and palliative care of CUP.