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Can expression of apoptosis genes, bcl-2 and bax, predict survival and responsiveness to chemotherapy in node-negative breast cancer patients?

BACKGROUND
Although the status of the axillary lymph nodes is widely accepted to be associated with prognosis in breast cancer patients, there is a need for biomarkers to be analyzed as indicators of responsiveness to treatment. The objective of this study was to test the hypothesis that the expression of apoptosis genes, bcl-2 and bax, predicts survival and responsiveness to chemotherapy in node-negative breast cancer patients.


METHODS
One hundred thirty premenopausal women with primary breast carcinoma were studied for the expression of bcl-2 and bax genes. The relationship between the expression of bcl-2 and bax proteins and a series of markers of known prognostic value [such as tumor size, nuclear grade, receptors of the steroid hormones estrogen (ER) and progesterone (PgR)]. The association of these proteins with survival and responsiveness to chemotherapy was also examined.


RESULTS
Sixty (46%) and sixty-four (49%) breast cancer cases were found positive for bcl-2 and bax, respectively, as indicated by immunohistochemistry. A statistically significant association was found between expression of bcl-2 and tumor size (P = 0.001), low grade (grade I) (P = 0.002), positivity of ER (P = 0.001), positivity of PR (P = 0.03), and superior disease-free survival (DFS) (P = 0.04), and superior overall survival (OS) (P = 0.03). In contrast, no similar associations were observed for the bax gene. Overall, there was a trend toward an association between adjuvant chemotherapy and DFS (P = 0.08) and OS (P = 0.07). This trend became statistically significant when the patients were analyzed by individual gene expression. In bax-positive patients, chemotherapy improves 6-year DFS (P = 0.01) and OS (P = 0.03) while similar effects were not observed in the other subgroups of patients.


CONCLUSION
Our results indicated that bcl-2 expression is associated with a number of favorable prognostic factors and better clinical outcome, while bax expression seems to have positive predictive value for responsiveness to chemotherapy in lymph node-negative breast cancer patients.