Progesterone-binding cyst protein (PBCP) in operable breast cancer: correlations with prognostic factors and predictive value for effect of adjuvant tamoxifen treatment.

Progesterone-binding cyst protein (PBCP) is a secretory protein which has been found in varying concentrations and incidence in cytosols from benign breast tumors, primary breast cancer and metastasis. In order to evaluate its correlation to other prognostic factors, PBCP was analysed in tumor cytosols from 386 women with stage I and stage II breast cancer. The incidence of PBCP negative (i.e. PBCP = 0) tumors was significantly decreased in node negative patients as compared to node positive (p = 0.012). An inverse correlation between estrogen receptor content and PBCP was found (p = 0.001). In a multivariate analysis PBCP category was found to be an independent predictor of the likelihood of axillary nodal involvement (p = 0.015). In spite of this association, PBCP did not reach statistical significance as an independent prognostic factor with regard to relapse-free survival. To evaluate PBCP category as a possible predictive factor for response to adjuvant endocrine treatment, a subpopulation of node positive patients with ER positive tumors was analysed; in patients with PBCP negative tumors, adjuvant treatment with tamoxifen proved to increase the relapse-free survival significantly (p = 0.011). We suggest that PBCP may have a place among other biochemical parameters in breast cancer, to provide an extended basis for understanding of tumor biology and a better selection of patients for endocrine treatment.