Steroid receptor interactions in human breast carcinoma.
Sucrose gradient centrifugation of estrogen and progestin receptors in cytosol preparations revealed that the majority of human breast tumors contained two molecular forms sedimenting at either 8S or 4S. Few tumors exhibited profiles containing predominately the 8S form or the 4S form alone. Molecular heterogeneity of the estrogen receptors in cytosol was demonstrated with regard to surface charge using ion-exchange chromatography and isoelectric focusing. The molecular properties of estrogen receptors in breast tumor biopsy specimens appear to be related to clinical responsiveness of patients given hormonal manipulations. These data and other findings related to the clinical utility of steroid receptor quantification impose a requirement for rigid quality control of analyses by the laboratory. The composition, evaluation, and distribution of tissue reference powders for establishing uniformity and quality control of steroid receptor analyses used in cooperative clinical trials of breast cancer treatment are described. This approach ensures meaningful correlations between laboratory results and clinical response.