Estrogen Receptor, Progesterone Receptor, and Human Epidermal Growth Factor Receptor 2 Expression Rates in Invasive Breast Carcinoma A Study of 21 Institutions

Context. - Laboratories performing predictive marker testing for breast carcinoma are encouraged to compare patient results to published benchmarks. Objective. - To collect expression rates for estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2) in invasive breast carcinoma from multiple laboratories. Design. - Participants submitted data from up to 50 primary cases during the study period. Participants reported ER, PgR, and HER2 results in addition to demographic and histologic information. Participants also provided annual institution-level expression rates. Results. - A total of 21 institutions submitted data for 687 cases. Aggregate positivity rates for ER and PgR were 85.6% and 75.1%, respectively. Receptor positivity rates were higher in well-differentiated (grade 1) tumors (ER, 97.4%; PgR, 88.0%) compared with moderately differentiated (grade 2) tumors (ER, 92.4%; PgR, 84.0%) and poorly differentiated (grade 3) tumors (ER, 61.8%; PgR, 48.0%). Expression rates were higher in postmenopausal women (ER, 87.2%) than premenopausal women (ER, 79.6%) and higher in lobular carcinomas (ER, 98.7%; PgR, 85.3%) than ductal carcinomas (ER, 84.1%; PgR, 74.5%). The aggregate HER2 positivity (score 31) rate was 9.0%. The aggregate HER2 equivocal (score 21) rate was 14.5%. Of 81 equivocal (score 21) cases, 70 (86.4%) were nonamplified. Conclusions. - The data from this study provide multiinstitutional benchmark data to assist laboratories performing periodic comparisons as part of a quality management program. Overall expression rates were generally similar to those of other published reports, with the exception of the ER-negative and HER2-positive rates, both of which were somewhat lower.