Variability of steroid receptors in multiple biopsies of breast cancer: effect of systemic therapy.

Estrogen receptor (ER) was measured on two or more specimens taken from each of 53 patients with carcinoma of the breast (18 also had progesterone receptor analyzed). Among the 35 patients who had no interval therapy, 27 patients had repeated tests within one month, and only two had reversal of ER results. Among the eight patients who had ER tests 9-36 months apart, four of five ER + lesions (7 + fmol/mg cytosol protein) had ER - metastasis. Among the 18 patients who received systemic therapy, three of ten ER + became ER -, while two of ten ER - became ER +. Our data and reports in the literature are summarized, showing that about 20% of receptor studies among multiple samples are different even when patients received no interval therapy. In asynchronous studies, it is more likely to have ER positive change to negative than vice versa (31% vs 12%). Interval chemotherapy or endocrine therapy tends to increase the occurrence of ER negative relapse among patients with ER positive tumors.