Galectin-9 as a prognostic biomarker in small cell lung cancer

Small cell lung cancer (SCLC) is a deadly tumor that is a highly aggressive and widely metastatic cancer, with a 7% 5-year survival rate (1). SCLC is one pathology type of lung cancer which also includes lung adenocarcinoma, lung squamous carcinoma and large cell lung cancer. Although SCLC accounts for approximately 15% of lung cancer patients, it has the poorest prognosis of all lung cancers. Although there has been much effort in conducting comprehensive molecular research (2), there have been no important therapeutic clinical advances for 30 years, leading SCLC to be designated as an intractable cancer (1). Furthermore, SCLC is a neuroendocrine tumor which has a relatively complex tumor microenvironment. Recently, immune checkpoint inhibitors play an important role in anti-tumor therapies for melanoma and renal cell carcinoma, bladder cancer, non-small cell lung cancer and others (3,4). However, there have been few studies to analyze the functions of immune checkpoints in the progression of SCLC