Progesterone Receptor Status Significantly Improves Outcome Prediction Over Estrogen Receptor Status Alone for Adjuvant Endocrine Therapy in Two Large Breast Cancer Databases

PURPOSE: To determine whether progesterone receptor (PgR) status provides additional value to estrogen receptor (ER) status and improves prediction of benefit from endocrine treatment among patients with primary breast cancer. PATIENTS AND METHODS: Clinical outcomes of patients in two large databases were analyzed as a function of steroid receptor status. The first database (PP), contained 3,739 patients who did not receive any systemic adjuvant therapy and 1,688 patients who received adjuvant endocrine therapy but no chemotherapy. The second database (SPORE), contained 10,444 patients who received adjuvant endocrine therapy but no chemotherapy. Biochemical ER and PgR assays were identically performed in two…