BACKGROUND: The costimulatory molecule B7-H1 (programmed death-1 ligand-1, PD-L1) has been implicated as a potential regulator of antitumor immunity in various human cancers. To date, no data are available on the role of B7-H1 in Barrett carcinoma. Therefore, we investigated the expression pattern and clinical significance of B7-H1 in a large cohort of patients with Barrett carcinoma. METHODS: Expression of B7-H1 was evaluated by immunohistochemistry in 101 patients with Barrett carcinoma. Expression data were correlated with clinicopathologic features, including TNM stage, UICC (Union Internationale Contre le Cancer) tumor stage, tumor grade, resection status, and survival, and with the number of tumor-infiltrating CD3(+), CD8(+), and CD45RO(+) T lymphocytes.RESULTS: Aberrant B7-H1 expression was found in Barrett carcinoma cells. High tumor B7-H1 expression was significantly associated with advanced T stage (p = 0.002), advanced UICC tumor stage (p = 0.022), and incomplete resection status (p = 0.009). The median survival of patients with high tumor B7-H1 expression was 38 months compared with 136 months for patients with no or low tumor B7-H1 expression. In the multivariable analysis, high tumor B7-H1 expression was significantly associated with an increased risk of death from Barrett carcinoma (hazard ratio, 3.50; 95% confidence interval, 1.66 to 7.38; p < 0.001). CONCLUSIONS: Our data suggest that B7-H1 may represent a new prognostic marker for patients with Barrett carcinoma. Furthermore, given its immune-inhibitory function, B7-H1 may represent a potential target in the treatment of Barrett carcinoma.