Estrogen and progesterone receptor levels are lower in specimens taken from previously biopsied breast tumor tissue.

Estrogen and progesterone receptor (ER and PgR) levels and peroxidase activity were measured in the first biopsy and in tissue removed 4-10 days later during mastectomy of previously biopsied tumor. The proportion of ER- and PgR-positive tumors declined from 71% and 63%, respectively, in the biopsy group, to 46% and 36% in the mastectomy group. Peroxidase activity was low or absent in all biopsy specimens, but was present in 16 out of 25 tumors which had been biopsied previously. Receptor levels in paired specimens obtained from the same patient were lower in the mastectomy in 14 out of 18 receptor-positive cases. This decrease in the receptor level was accompanied by a significant increase in peroxidase activity. We suggest that an attempt be made to perform receptor analysis from "virgin" tumor tissues at initial biopsy. If this is not possible, measurement of peroxidase activity could be helpful in evaluating the degree of receptor deterioration.