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Apoptosis and expression of apoptosis-regulating proteins, Bcl-2 and Bax, have been observed in human breast carcinomas. The authors investigated whether expression of Bcl-2 and Bax proteins and apoptotic index (AI) had significance in cases of primary breast cancer. The authors evaluated Bcl-2 and Bax immunoreactivity and AI in primary breast cancers with the ApopTag method in 91 breast cancer patients retrospectively with long-term follow-up (median 60 months). Bcl-2 expression was seen in 60 (65.9%) cases and Bax expression was observed in 59 (64.8%) cases. Increased Bcl-2 and absence or low Bax immunoreactivity were significantly associated with low AI, high tumor grade, axillary lymph node involvement, postoperative recurrence, and metastasis. Thirty-five (38.5%) samples expressed high AI, which correlated with low tumor grade, absent axillary lymph node metastasis, and low levels of Bcl-2 with Bax overexpression. In univariate analysis, the variables associated with short relapse-free survival (RFS) and overall survival (OS) were large tumor size, axillary lymph node involvement, high histologic grade, low AI, high Bcl-2 expression, and absence or low Bax expression. In multivariate analysis, only Bcl-2 expression, lymph node status, and histologic grade were of independent prognostic value with respect to RFS and OS. Because the vast majority of the patients in this study received chemotherapy, it can be concluded that these apoptotic markers were also predictive of response to chemotherapy. Immunostaining of apoptosis-related genes, Bcl-2 and Bax, together with AI, may stratify high- versus low-risk breast cancer patients. [ABSTRACT FROM AUTHOR]