The underlying basis for cancer immune evasion is important for effective immunotherapy and prognosis in breast cancers. Human leucocyte antigens (HLA)-I comprising three classical antigens (HLA-A, -B and -C) is mandatory for anti-tumor immunity. Its loss occurred frequently in many cancers resulting in effective immune evasion. Most studies examined HLA-I as a whole. Alterations in specific locus could have different clinical ramifications. Hence, we evaluated the expression of the three HLA-I loci in a large cohort of breast cancers. Low expression of HLA-A, -B and -C were found in 71.1%, 66.3%, and 60.2% of the cases. Low and high expression in all loci was found in 48.3% and 17.9% of the cases respectively. The remaining showed high expression in one or two loci. Cases with all HLA high expression (all HLA high) was frequent in the ER-HER2- (27.4%) and ER-HER2+ (23.1%) cases and was associated with characteristic pathologic features related to these tumor (higher grade, necrosis, high tumor infiltrating lymphocyte (TIL), pT stage, low hormonal receptor, high basal marker expression) (p ≤ 0.019). Interestingly, in HER2+ cancers, only cases with all HLA high and high TIL showed significantly better survival. In node positive cancers, concordant high HLA expression in primary tumors and nodal metastases was favorable prognostically (DFS: HR = 0.741, p < 0.001; BCSS: HR = 0.699, p = 0.003). The data suggested an important clinical value of a combined analysis on the co-expression HLA-I status in both primary and metastatic tumors. This could be a potential additional key component to be incorporated into TIL evaluation for improved prognostication.
Keywords: Breast cancer; HER2+; HLA loci; Immunohistochemistry; Survival.