Aim: To assess the value of immunohistochemistry in discriminating between BRCA1 associated and non-BRCA1 associated breast tumours.
Methods: Four commercially available anti-BRCA1 antibodies were used on 45 paraffin wax embedded tumoral samples from patients with (seven of 45) and without (38 of 45) BRCA1 germline mutations. In all patients, the BRCA1 gene had been studied previously by means of the protein truncation test (PTT), conformational sensitive gel electrophoresis (CSGE), and direct sequencing of genomic DNA. Immunohistochemistry was carried out using the standard avidin-biotin immunoperoxidase method. Antigen retrieval was carried out by means of microwave pretreatment or autoclaving. The antibody panel used comprised D-20 (1/500), I-20 (1/100), K-18 (1/100), and MS110 (Ab-1; 1/50).
Results: No immunohistochemical differences in BRCA1 protein expression were found between cases with and without BRCA1 germline mutations. All positive cases showed predominantly cytoplasmic staining, in both tumoral and non-tumoral cells, with the polyclonal antibodies D-20, I-20, and K-18. After heating pretreatment both nuclear and cytoplasmic staining were found in tumoral and non-tumoral cells with the I-20 antibody. Only the monoclonal antibody MS110 showed a predominantly nuclear staining after microwave oven treatment.
Conclusions: Commercially available BRCA1 antibodies lack the specificity required to identify the BRCA1 protein and thus are not useful for establishing differences between familial and sporadic breast tumours, or between BRCA1 associated and non-BRCA1 associated breast tumours.