The usefulness of antibodies to the BRCA1 protein in detecting the mutatedBRCA1 gene. An immunohistochemical study

Aim-To assess the value of immunohistochemistry in discriminating between B RCA1 associated and non-BRCA1 associated breast tumours. Methods-Four commercially available anti-BRCA1 antibodies were used on 45 p araffin wax embedded tumoral samples from patients with (seven of 45) and w ithout (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 genornic DNA. Immunohistochemistry was carried out using the standard a vidin-biotin immunoperoxidase method. Antigen retrieval was carried out by means of microwave pretreatment or autoclaving. The antibody panel used com prised 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 positiv e cases showed predominantly cytoplasmic staining, in both tumoral and non- tumoral cells, with the polyclonal antibodies D-20, I-20, and K-18. After h eating pretreatment both nuclear and cytoplasmic staining were found in tum oral and non-tumoral cells with the I-20 antibody. Only the monoclonal anti body MS110 showed a predominantly nuclear staining after microwave oven tre atment. Conclusions-Commercially available BRCA1 antibodies lack the specificity re quired to identify the BRCA1 protein and thus are not useful for establishi ng differences between familial and sporadic breast tumours, or between BRC A1 associated and non-BRCA1 associated breast tumours.