Estrogen receptor negative and progesterone receptor positive primary breast cancer: pathological characteristics and clinical outcome. Institut Curie Breast Cancer Study Group.

The expression of estrogen (ER) and progesterone (PgR) receptors was analyzed in a retrospective series of 3000 patients who had operable primary breast cancer. Patients were stratified according to ER and PgR status and the study was focused on the two groups (ER-PgR+ and ER-PgR-) of patients whose tumors contained low levels of ER (< 15 fmol/mg protein), regarding potential response to endocrine therapy. The comparison of clinical or histological characteristics between ER-PgR+ and ER-PgR- patients was analyzed as well as the disease-related death and survival. The mean follow-up was 86.3 months. Among the 529 ER-patients, 62 were PgR+ (12%), whereas 467 were PgR- (88%). The ER-PgR+ and ER-PgR- populations represented 2% and 15.6% of the overall population, respectively. In ER- tumors, the PgR status was significantly related to: age, menopausal status, tumor size, SBR grade, and histological type, but not to the type of surgical treatment or to lymph node involvement. ER-PgR+ tumors had smaller size (64% T1 vs 43%) (p=0.004) and were more frequently grade I (28% vs 12%) than ER-PgR- tumors (p < 0.001). In addition, the patients with ER-PgR+ tumors were significantly younger (49.4 years vs 58.4 years; p < 0.0001), and were more frequently premenopausal (76% vs 36%, p < 0.001). The disease-free interval and the metastasis-free survival tended to be worse for ER-PgR- than for ER-PgR+ patients, but the difference was not statistically significant at 10 years. However, a small but significant difference in overall survival, in favor of the PgR+ group, was observed between the two groups during the first 5 years (p=0.03). We conclude that in combination with ER, PgR status defines a group of patients with clinical and biological specificity, which could be considered for specific endocrine therapy.