Expression of a novel immune checkpoint B7-H6 ligand in human small cell lung cancer

BACKGROUND: B7-H6 is a novel co-stimulatory ligand that is detected in most malignancies. However, the significance of B7-H6 in small cell lung cancer (SCLC) remains unknown. METHODS: B7-H6 expression was analyzed by immunohistochemistry (IHC) in 103 collected SCLC samples, and its association with clinicopathological characteristics and prognosis was analyzed. The 2-year survival rates were also investigated. RESULTS: B7-H6-positive staining was detected in 58 (56.31%) SCLC cases, and found to be localized mainly in the intracellular space of SCLC. Weak staining in lung tissues was observed in 4 (8%) cases. B7-H6 positive staining was significantly related to tumor-node-metastasis stage (P=0.028), age (P=0.001), and distant metastasis (P=0.033), whereas there was no association with smoking status, sex, mass size, limited-stage SCLC/extensive-stage SCLC, Karnofsky performance status, or nodal metastasis status. The 2-year survival rates showed that there were more patients whose survival was shorter than 2 years in the B7-H6-positive group compared with the B7-H6-negative group (P=0.042). CONCLUSIONS: Our findings suggest that B7-H6 is involved in early-stage SCLC and could serve as an early marker to predict human SCLC progression and distant metastasis. B7-H6 may be a valuable therapeutic target with potential clinical applications in the future.