Investigation is lacking regarding the clinical impact of human leukocyte antigen (HLA) class I downregulation in breast cancer and results are inconsistent. In this study, we investigated the expression of HLA class I, the heavy chain, and beta2-microglobulin (beta2-m) by immunohistochemistry in 67 breast carcinomas (BC) and correlated results with clinical-pathologic parameters and patient outcomes. Seventy-six percent of BC were downregulated for HLA class I, whereas downregulation of heavy chain and beta2-m was observed in 57 and 46% of BC, respectively. A significant association existed between the absence of tumor necrosis and downregulation of class I and beta2-m and between the absence of lymphovascular invasion and patient's age and downregulated class I and heavy chain, respectively. Among the lymph node-positive BC patients, a significantly improved overall survival was observed in those showing beta2-m downregulation compared with patients with normal beta2-m. This result may correlate with the role of beta2-m in regulating cancer cell growth.