The aim of the present study was to characterize the expression pattern of tumor necrosis factor (TNF)-alpha and its receptors in breast samples (benign diseases, in situ carcinomas and infiltrating carcinomas), and to compare these results with those obtained previously for interleukin-6, p53 and p21 using the same samples in order to elucidate the effects of these cytokines on the proliferation-apoptosis equilibrium. Immunoexpression of TNF-alpha and its receptors (TNFRI and TNFRII) were studied by western blotting and immunohistochemistry. The percentage of samples positive for TNF-alpha and TNFRII was higher in in situ carcinoma than in benign breast diseases, and TNFRII was even higher in infiltrating tumors. The percentage of samples positive for TNFRI was similar in the three groups. For the three proteins and in the three patient groups, immunoreactions were observed in the peripheral cytoplasm. In the positive samples, immunostaining for TNF-alpha was more intense in infiltrating tumors than in the other two patient groups, whereas immunostaining for both receptors was higher in in situ carcinoma than in benign breast diseases, and even higher in infiltrating tumors. Comparing the TNF-alpha results with previous results for mtp53, p21 and interleukin-6, we found an association between the expression of these four proteins and increasing malignancy. TNF-alpha might be an important factor in breast cancer promotion as its proliferation and survival effects seems to be enhanced through the increased expression of TNFRII. Also, the pro-apoptotic pathway of TNFRI could be inhibited by p21 (which appeared increased in breast cancer), altering TNFRI effects in promoting the expression of several factors, such interleukin-6, which contribute to tumor promotion.