The determination of progesterone receptors in breast cancer and their relationship to estrogen receptors.

A simple method for the assay of specific progesterone receptors in breast cancer tissue is described. Progesterone receptors were detected in 63 of 74 breast cancer specimens (85%). Estrogen receptor positive tumors had a wide range of progesterone receptor concentrations, but in 77% of cases the level was above 3 fmol/mg protein. The progesterone receptor level was generally low in tumors lacking estrogen receptors, 75% of the samples having concentrations between 0 and 3 fmol/mg protein. Unlike estrogen receptors, age had no influence on the number of progesterone receptors in breast cancer tissue.