Relation of tumor content of estrogen and progesterone receptors with response of patient to endocrine therapy.

The levels of estrogen (E2R) and progesterone (PgR) receptors in 165 breast tumor biopsies have been determined. Seventy-seven percent of the specimens contained significant levels of E2R; 38.2% were positive for both receptors. Only four tumors displayed the unusual E2R=/PgR+ pattern. Tumors from pre- and postmenopausal patients had similar receptor characteristics. Two-thirds of the six patients with E2R+PgR+ tumors responded to hormonal therapy, whereas only 28.7% of the E2R+/PgR- tumors regressed after similar treatment. These data from a limited number of patients indicate that the presence of E2R and PgR in breast tumor biopsies is of higher prognostic value for response of the patient than in the presence of E2R alone.