Standardization of estrogen-receptor analysis by immunohistochemistry: An assessment of interlaboratory performance in Ireland

Multiple Irish histopathology laboratories are beginning to offer estrogen-receptor (ER) assessment by immunohistochemical analysis. However, interlaboratory comparison and standardization has not been performed. In this study, Irish hospitals were surveyed to obtain detailed information regarding their immunostaining protocol. Each participating laboratory (n = 16) was supplied with 10 sections of breast tumors to immunostain by their method, which were then quantified by three assessors. The survey revealed that four methods of antigen retrieval were in use: microwaving (10 of 16), pressure cooker (four of 16), autoclave (one of 16), and hot oven (one of 16); microwaving in citrate solutions was the commonest method. Citrate buffer and antibody clone ID5 were used by all participants with substantial variation in antibody dilution (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 supplied sections. However, variation in intensity of immunostaining, focal staining, and weak nuclear counterstaining were observed. Recommendations from this survey were that every hospital join an external quality-assessment scheme, hospitals with poor detection of ER immunopositivity review their techniques, and that a weakly ER-positive tumor be included with all immunohistochemistry runs.