['Immunotherapy with antibodies against B7/CD28 family members, including PD-1, PD-L1, and CTLA-4 has shifted the treatment paradigm for non-small-cell lung carcinoma (NSCLC) with improved clinical outcome. HHLA2 is a newly discovered member of the family. By regulating T-cell function, HHLA2 could contribute to tumor immune suppression and thus be a novel target for cancer immunotherapy. There is limited information and critical need to characterize its expression profile and clinical significance in NSCLC.', 'We performed immunohistochemistry with an HHLA2-specific antibody (clone 566.1) using tissue microarrays constructed from 679 NSCLC tumor tissues, including 392 cases in the discovery set and 287 cases in the validation cohort. We also studied clinico-pathological characteristics of these patients.', 'Overall, HHLA2 was not detected in most of normal lung tissue but expressed in 66% of NSCLC across different subtypes. In particular, EGFR-mutated NSCLC was significantly associated with higher tumor HHLA2 expression in both discovery (EGFR vs. WT: 76% vs. 53%, P=0.01) and validation cohorts (89% vs. 69%, P=0.01). In one of the two cohorts, HHLA2 expression was higher in lung adenocarcinoma as compared to squamous and large cell histology, non-Hispanic White vs. Hispanics, and tumors with high tumor infiltrating lymphocyte (TIL) density. In the multivariate analysis, EGFR mutation status and high TIL intensity were independently associated with HHLA2 expression in lung adenocarcinoma.'] Is hHLA2 , a new immune checkpoint member of the B7 family , widely expressed in human lung cancer and associated with EGFR mutational status?