Immunofluorometric study of Bcl-2 and Bax expression in clinical fresh tumor samples from breast cancer patients

The balance between the expression of the antiapoptotic gene Bcl-2 and the proapoptotic gene Bax is considered a good indicator of the apoptotic activity of tumor cells. Bcl-2 and Bax expression seem also to individually play a prognostic role in breast cancer. Our aim was to study the expression of both genes in fresh breast cancer samples, and to correlate the obtained results with other available clinical and biological parameters of the tumors.

Fresh tumor specimens from 86 breast cancer patients were studied by means of immunofluorocytometry for the expression of the apoptosis-associated Bcl-2 and Bax genes. Additionally, DNA-ploidy was also measured. Paraffin blocks corresponding to the same tumors were used for immunohistochemistry, to study the expression of hormone receptors (ER and PR), p53, c-erb-B2 and the Ki67 labelling index. Fourteen patients had been treated with four cycles of induction chemotherapy (cyclo-phosphamide, adriamycin and 5-fluorouracil), and separate statistical analyses were carried out both for the whole group, and for the 62 patients not having received any treatment whatsoever, in order to exclude any potential influence of the chemotherapeutic treatment on the expression of the studied antigens.

Bcl-2 expression correlated significantly with estrogen (p = 0.002) and progesterone (p = 0.012) receptor expression, as well as with c-erb-B2 (p = 0.045) expression in chemotherapy-naïve tumors, the correlation being completely lost if treated tumors were added to the study group. A high apoptotic index (Bcl2/Bax < 0.5) correlated significantly with progesterone receptor expression (p = 0.037) and c-erb-B2 expression (p = 0.018), and this correlation was maintained, whether previously treated tumors were included into the study or not (p = 0.038 and p = 0.027, respectively). Bax expression did not correlate with any other clinical or biological parameters of the tumors, including Bcl-2 expression.

Bcl-2 and Bax-expression can be easily determined in clinical breast cancer specimens by means of immunofluorocytometry. Bcl-2-expression significantly correlates with hormone-receptor- and c-erb-B2-expression exclusively in previously untreated tumors. This, however, seems only to be the case when considering Bcl-2 expression in isolation, since a high apoptotic index, which considers the ratio of Bcl-2 versus Bax expression in the same tumor, seems not to be affected by the previous use of chemotherapy.