A minimally invasive assay detects BRCA 1 germline mutations

Previously, we described an antibody based assay which detects BRCA 1 gene alterations in surgical specimens from individuals with ovarian cancer. We also reported that this assay can detect BRCA 1 expression in human buccal cells and demonstrated BRCA 1 transcription in these cells using RT-PCR. To determine whether this antibody based assay can detect protein truncations resulting from germline BRCA 1 gene mutations in buccal cells, a study was conducted in which immunohistochemical reactivity was compared with BRCA I genetic analysis. Buccal cells of three individuals at high risk for developing heritable breast or ovarian cancer were collected. Mutation analysis was performed using PCR and SSCP followed by gene sequencing of unique polymorphisms. Immunohistochemical analysis of cytospin deposited buccal cells was performed using antibodies directed at the amino and carboxy ends of the BRCA 1 protein. In two of three specimens, germline mutations were detected. This was consistent with the immunohistochemical results which showed reduced reactivity with the carboxy binding antibody, suggesting the presence for a protein truncation. In the third specimen, no BRCA 1 polymorphisms were detected and immunohistochemical reactivity for the amino and carboxy termini were similar to the controls. We conclude that this immunohistochemical assay using buccal cells may serve as a minimally invasive, clinical tool to detect germline BRCA 1 gene mutations.