STANDARDIZATION OF ESTROGEN-RECEPTOR ANALYSIS BY IMMUNOHISTOCHEMISTRY- AN ASSESSMENT OF INTERLABORATORY PERFORMANCE IN IRELAND

Multiple Irish histopathology laboratories are beginning to offer estr ogen-receptor (ER) assessment by immunohistochemical analysis. However , interlaboratory comparison and standardization has not been performe d. In this study, Irish hospitals were surveyed to obtain detailed inf ormation regarding their immunostaining protocol. Each participating l aboratory (n = 16) was supplied with 10 sections of breast tumors to i mmunostain by their method, which were then quantified by three assess ors. The survey revealed that four methods of antigen retrieval were i n use: microwaving (10 of 16), pressure cooker (four of 16), autoclave (one of 16), and hot oven (one of 16); microwaving in citrate solutio ns was the commonest method. Citrate buffer and antibody clone ID5 wer e used by all participants with substantial variation in antibody dilu tion (1:20 to 1:100) and incubation time (20 minutes to overnight). No superheating method provided superior immunostaining. The majority of participants achieved acceptable immunopositive staining in the suppl ied sections. However, variation in intensity of immunostaining, focal staining, and weak nuclear counterstaining were observed. Recommendat ions from this survey were that every hospital join an external qualit y-assessment scheme, hospitals with poor detection of ER immunopositiv ity review their techniques, and that a weakly ER-positive tumor be in cluded with all immunohistochemistry runs.