Single-point versus five-point biochemical method for determination of estrogen and progesterone receptors

Receptors for estrogen and progesterone are accepted by international consensus as biomarkers of breast carcinoma responsiveness to endocrine therapy. Numerous current studies are aimed at consideration of importance of "the new generation" of estrogen-regulated biomarkers in treatment of breast cancer patients. Simultaneous knowledge of all these biomarkers may help in medical decision making. However, the amount of tumor material available from breast carcinoma can make impossible determination of estrogenregulated biomarkes together with estrogen and progesterone receptors. To assess whether we could replace our current five-point ligand binding assay for measurement of estrogen and progesterone receptors with a single- point ligand binding assay, we compared simultaneous measurements in same samples of breast carcinomas by both methods. A linear regression analysis shows that single-point assay can be confidently used instead of five-point assay. In addition, there were no variations over time in estrogen and progesterone receptors phenotypes, as well as in estrogen and progesterone receptors contents determined by single-point assay. Accordingly, the results clearly demonstrate the validity of intralaboratory quality control and give a possibility for the establishment of interlaboratory quality control of single-point ligand binding assay.