A multi-institutional study of interlaboratory variance in the estrogen and progesterone receptor assays

Purpose: The expression of hormone receptors is the most reliable factor for predicting the responsiveness to hormonal therapy. At present, immunohistochemistry (IHC) is considered as a practically reliable method. This study was designed to examine the interlaboratory variance in immunohistochemical assays for estrogen receptor (ER) and progesterone receptor (PR) in Korea. Methods: The Korean Study Group for Breast Pathology (KSGBP) made a questionnaire to know the current situation in HR assay in Korea. The questionnaire was sent to the members of KSGBP by e mail, which were included eight questions relating to tissue handling, ER/PR IHC procedure and interpretation method. Forty laboratories replied with the completed questionnaire. Results: All 40 laboratories were using formalin as a fixative. Pretreatment was performed using six different methods including autoclave (25%), microwave (30%) and full autostainer (15%). Primary antibodies for ER were SP1 in 40%, 6F11 in 27.5% and 1D5 in 32.5%. Primary antibodies for PR were more variable (seven clones) than those for ER. Interpretation method used was Allred system in 20%, modified Allred system in 15%, report the % of positive tumor cells in 45%, positive/ negative in 15% and others in 5%. The expression rate of ER was ranged from 45.6% to 93% (mean 63.5%) and the expression rate of PR was ranged from 27% to 90% (mean 59.1%). The differences according to the numbers of breast cancer in each institute, primary antibodies, detection systems and interpretation methods did not influence to the expression rate of ER/PR, statistically (p>0.05). Conclusion: In Korea, the interlaboratory variance in ER/PR IHC procedure was too huge to make a standardized method. We suggest the proper quality control program such as ER/PR staining with positive internal and external controls and negative control might be better to aim at getting similar results among the different laboratories rather than trying to standardize the procedure.