The B7-H1 (PD-L1) T lymphocyte-inhibitory molecule is expressed in breast cancer patients with infiltrating ductal carcinoma: Correlation with important high-risk prognostic factors

B7-H1 molecule increases the apoptosis of tumor-reactive T lymphocytes and reduces their immuno-genicity. Breast cancer is the second most common cause of mortality after lung cancer. Direct evidence linking B7-H1 with cancer has been shown in several malignancies; however, its expression in breast cancer has not been investigated. We used immunohistochemistry to investigate the expression of the B7- H1 molecule in 44 breast cancer specimens and to study its correlation with patients' clinicopathological parameters. The expression of B7- H1 was shown in 22 of 44 patients and was not restricted to the tumor epithelium ( 15 of 44, 34% in tumor cells), but was also expressed by tumor-infiltrating lymphocytes (TIL; 18 of 44, 41%). Interestingly, intratumor expression of B7- H1 was significantly associated with histologic grade III-negative ( P =.012), estrogen receptor-negative ( P = .036), and progesterone receptor-negative ( P = .040) patients. In addition, the expression of B7- H1 in TIL was associated with large tumor size ( P = .042), histologic grade III ( P =.015), positivity of Her2/neu status ( P = .019), and severe tumor lymphocyte infiltration ( P = .001). Taken together, these data suggest that B7-H1 may be an important risk factor in breast cancer patients and may represent a potential immunotherapeutic target using monoclonal antibody against the B7- H1 molecule.