Sampling procedures in estrogen receptor determinations.

To determine the significance of proteolysis and delayed freezing of tumor samples on estrogen receptor levels, values from 19 of 31 biopsy specimens were compared with that in remaining tumor at the completion of mastectomy. There was a 15-100% decrease in receptor content. Time-decay studies on selected postmastectomy samples showed a further decrease in estrogen receptor content inversely proportional to the time it was exposed to room temperature. Factors that govern the valid measurement of receptor levels include tumor cell concentration, tumor necrosis, and time between devascularization of the specimen to freezing. A carefully procured histologically confirmed sample of fresh tumor is necessary for reliable estrogen receptor values.