Quality control for estrogen receptor quantification by dextran-coated charcoal assay: a single laboratory's experience.

Wide fluctuations in results obtained by different laboratories for the content of estrogen receptors from a single source of tissue powder were reported by several investigators at the 1979 NCI Consensus Committee Meeting for Steroid Receptors in Breast Cancer and were further supported by data collected by our laboratory for the Eastern Cooperative Oncology Group. In a multilab study the inconsistency in the receptor content is a product of the variations associated with the assay procedures used by different laboratories and those due to unavoidable daily changes in the experimental conditions within each laboratory. In this report we present data on the variation of estrogen receptor measurements obtained by a single laboratory for any single source of tissue powder repeatedly analyzed. A retrospective analysis of the data collected on the receptor content of several different batches of calf uteri analyzed on different days (inter-assay variation) under uniform conditions revealed a coefficient of variation averaging +/- 35% (standard deviation divided by mean X 100). Experiments showed that the fluctuations in the receptor yield from aliquots of the same tissue powder are primarily an effect of the homogenization step that precedes cytosol preparation. Therefore, for establishing quality control, distribution of lyophilized cytosols should precede lyophilized powders to test the efficiency of performance of laboratories. A homogenizer designed to minimize thermal denaturation is also essential.