Precision in estrogen and progesterone receptor assays. Results of the first CAP pilot survey

In this blind survey involving 47 unselected laboratories, 98% of participants concurred that a nominally mid-range estrogen receptor (ER) positive powder was positive; the concurrence was 91% for the progesterone receptor (PR). This precision exceeds the requirements imposed by the benefit: cost ratios which exist for the hormonal therapy of advanced breast cancer. In the same blind survey, the concurrence on nominally negative ER and PR specimens was 92% and 90%, respectively. These are also quite acceptable for the clinical context in which these tests are applied. Powders of human breast carcinoma are suitable for interlaboratory quality control. The particular lyophilized products we used were not as satisfactory.