California Breast Cancer Research Program

Bax and Bcl-2 are proteins that regulate programmed cell death and apoptosis. The expression of these proteins can be regulated, at least in part, by the tumor suppressor p53, but the effects of p53 are highly tissue specific. In an effort to better understand the relation between p53 and the in vivo control of the expression of Bax and Bcl-2 in adenocarcinomas of the breast, we evaluated by immunohistochemistry the expression of Bcl-2 and Bax in 149 invasive ductal carcinomas, 135 of which were chosen because of their p53 immunopositivity. The percentages of Bcl-2-immunopositive tumor cells were significantly lower in the p53-positive (median 20%) subsets as compared to the p53-negative (median 85%) subsets (P = 0. 004). Comparisons of the percentages of p53-immunopositive tumor cells with the percentages of Bcl-2- and Bax-positive cells (as continuous variables) revealed a significant inverse correlation between Bcl-2 and p53 (r = -0.41, P < 0.001) but not between Bax and p53. In the p53-positive subset, the percentages of Bax- and Bcl-2-immunopositive tumor cells were correlated positively (r = 0. 27, P = 0.002), suggesting that the expression of these genes may be co-regulated to some extent in these breast cancers. Higher percentages of Bcl-2-positive tumor cells were also associated with estrogen receptor positivity (P = 0.03), low histological tumor grade (P = 0.03), and low T stage (P = 0.02), whereas Bax immunostaining was associated only with c-erbB-2 immunopositivity (P = 0.02). Although the number of cases was small and treatment was non-uniform, preliminary correlations with clinical outcome data suggest that the prognostic significance of Bcl-2 may be enhanced by inclusion of Bax data in patients with p53-immunopositive adenocarcinoma of the breast, at least for patients with node-negative disease. Taken together, these data suggest that, despite the ability of p53 to bind directly to the Bax gene promoter, the regulation of Bax in human breast cancers does not necessarily correlate with p53 status, implying that regulation of this pro-apoptotic gene in these tumors is complex and probably influenced by several factors.