Hormone receptors in breast cancer. Analytic accuracy of contemporary assays.

When powders of human breast carcinomas were assayed by an unselected group of laboratories, there was 90% to 98% concurrence in estrogen and progesterone receptor results. While these results demonstrate room for improvement in assay technique, it is clear that the variability due to the analysis does not exceed the variability of the clinical course and the clinical assessment of the conditions of patients with breast cancer.