Apoptosis may play a major role in determining tumor growth and aggressiveness. The aim of this study was to examine the relationship between apoptosis, expression of bcl-2 and p53 proteins, proliferation index, and other clinicopathological features of breast carcinoma. Sixty-five formalin-fixed paraffin-embedded tissue sections from invasive ductal breast carcinomas were studied for the presence of apoptosis by the terminaldeoxynucleotidyl-transferase-mediated dUTP-FITC nick end-labeling (TUNEL) method. Immunohistochemical methods were also used to determine the expression of estrogen receptor, Ki67, bcl-2 and p53 proteins. The number of apoptotic cells ranged from 2.0 to 236.0/10HPF (mean 36.26, median 28.0). The observation of 30 apoptotic cells/10HPF was more common in tumors > 3 cm, of histological grade III, with a high mitotic index, Ki67 index > or = 300, and p53 positivity; however, statistical significance was found only for the histological grade. Grade I and III tumors displayed an inverse association between the apoptotic index and bcl-2 and p53 protein expressions; grade I tumors frequently expressed bcl-2 (19/28), lacked p53 (20/28), and presented a low number of apoptotic cells (18/28), whereas grade III tumors tended to express p53 (12/17), lacked bcl-2 (13/17), and displayed a high number of apoptotic cells/10HPF (12/17). Multivariate analysis for survival revealed that estrogen receptors and apoptosis were independent variables. These data suggest that apoptosis, rather than proliferation index or expression of bcl-2 or p53 proteins, is an independent factor for the prognosis of survival.