Apoptosis in breast carcinomas detected with monoclonal antibody to single-stranded DNA: relation to bcl-2 expression, hormone receptors, and lymph node metastases.

Precise quantitation of apoptotic cells in solid tumors is necessary to determine the role of apoptosis in cancer growth, prognosis, and treatment. In this study, the intensity of apoptotic death was determined in 91 breast carcinomas with a novel cellular marker of apoptosis based on the staining of histological sections with a monoclonal antibody (MAb) to single-stranded DNA. Staining of apoptotic cells with the MAb reflected the decreased thermal stability of DNA induced by the digestion of nuclear proteins, as demonstrated by the elimination of staining in sections reconstituted with histones before heating. The high sensitivity and specificity of apoptosis analysis with the MAb is based on the central role of protease activation in the mechanism and control of apoptosis. Apoptotic indexes (AIs) in breast carcinomas ranged between 0 and 46%. Most of the carcinomas had relatively low AIs, whereas 29 cases were classified as carcinomas with intensive apoptosis (AI >/= 10%). The high level of apoptotic cell death was associated with negative immunostaining for bcl-2 protein, the loss of estrogen and progesterone receptors, high proportion of cells in S-phase, and increased risk of lymph node metastases. There was no correlation between AI and tumor size or p53 immunostaining. Lymph node metastases were detected in 59% of patients with high levels of apoptosis in primary carcinomas and in only 21% of patients with AIs below 10% in primary carcinomas. Thus, the high sensitivity of the MAb assay made it possible to identify a subset of breast carcinomas with intensive apoptosis and markers of poor prognosis. These results demonstrate that the measurement of apoptosis in breast carcinomas provides valuable prognostic information.