Reliability of clinical estrogen receptor assays performed on tumor tissue biopsied from sites previously treated with radiotherapy

The present retrospective analysis was done to determine whether previous radiotherapy to a biopsy site could be a source of false-negative estrogen receptor assays as suggested in earlier reports. The present study population included 56 women who had estrogen receptor assays done on tumor tissue obtained from skin, subcutaneous, or lymph node metastases. Tissue was taken from a previously irradiated area in 14 patients and from an unirradiated area in 42. Fifty-seven percent of the former and 50% of the latter patients had positive estrogen receptor assays, and quantitative levels of estrogen receptor also were comparable between the two populations. Other potential variables, including age, menopausal status, disease-free interval, dominant metastatic site, prior cytotoxic chemotherapy, and extent of disease, also were analyzed, but did not significantly alter interpretation of results. Patients in both irradiated and unirradiated groups who had low tumor-to-stroma ratios histopathologically were less likely to have positive estradiol receptor assays than patients with more cellular tumors (25% vs. 70%). In the present series it did not appear that prior radiotherapy to a site biopsied for estrogen receptor assay resulted in false-negative determinations. These observations require confirmation in large comparative series of patients.