Progesterone binding cyst protein in hormone receptor positive breast cancer; a predictive factor for effect of adjuvant tamoxifen treatment

Progesterone binding cyst protein (PBCP) was measured in breast cancer cytosols from 128 pre- and post-menopausal women with operable node positive (pN+) breast cancer Stage II. All patients were included in a national multicenter study on the effect of adjuvant tamoxifen treatment in hormone sensitive breast cancer, i.e. estrogen receptor content of at least 10 pmol/g cytosol protein. Patients were randomised to receive adjuvant tamoxifen 20 mg once daily for two years or no endocrine treatment. At a median follow-up of 60 months, we found PBCP content in the primary tumor to be an important factor with regard to the effect of adjuvant tamoxifen treatment. The benefit of adjuvant tamoxifen treatment on relapse-free survival and overall survival was confined to the subpopulation of patients with PBCP negative tumors. PBCP should be further evaluated as a predictive factor for the effect of tamoxifen treatment