Multiple simultaneous and sequential estrogen receptor values in patients with breast cancer.

Fifty-nine women had multiple estrogen receptor assays done, either simultaneously or sequentially. Eighty-six percent of the patients who had multiple synchronous estrogen receptor assays from various metastatic sites showed no significant discrepancy in estrogen receptor values. When estrogen receptor assays were done sequentially without intervening therapy, 83.5 percent of the patients maintained their initial positivity or negativity. However, when the second estrogen receptor determination was preceded by either chemotherapy or hormonal therapy, 33 percent of the patients had a significant discrepancy in estrogen receptor values. The most common discrepancy was estrogen receptor-positive tumors becoming estrogen receptor-negative, although a small number of patients were found whose receptor values became more positive after hormonal ablation.