Predictive value of estrogen receptor status as assessed by ligand-binding assay in patients with early-stage breast cancer treated with breast conserving surgery and radiation therapy.

It is important to determine which factors are predictive for the prognosis of patients treated with breast conserving surgery (BCS) and radiation therapy (RT) in order to make a decision as to the adjuvant treatment. Although estrogen receptor (ER) is known to be a predictive marker for antiestrogens in breast cancer, the prognostic effect of hormone receptors has not been fully analyzed in Japanese breast cancer patients treated with BCS and RT. A total of 153 breast cancer patients having up to three positive nodes in the axilla as identified histologically and treated with both BCS and RT with or without systemic therapy were enrolled in this study. All tumors were measured for ER and progesterone receptor (PR) using ligand-binding assay (LBA). ER was inversely related to patients' age, however, PR was not related to any clinical features. When ER was classified into negative, weakly positive and strongly positive categories, with cut-off levels of zero and 50 fmol/mg protein, the relapse-free survival (RFS) was significantly better in patients with tumors having strongly positive ER than in patients with tumors having negative ER. Multivariate analysis revealed that ER as well as nodal status, was an independent predictive factor for RFS, however, PR was not. As a result, we believe that ER measured by LBA is valuable for predicting prognosis of early-stage breast cancer patients treated with BCS and RT.