Loss of heterozygosity at the BRCA2 locus is a common finding in prostate cancer in men with a germline BRCA2 mutation

Abstract

10539 Background: The prevalence of prostate cancer (PC) is higher in men with a germline mutation in BRCA2 and to a lesser extent BRCA1. It is unclear as to whether a causal relationship exists between these mutations and PC tumorigenesis. The primary aim of this pilot study was to examine for loss of heterozygosity (LOH) in PC samples from men with a known BRCA1/2 mutation. Secondary aims included assessment of the clinical and pathological features of PC in these individuals. Methods: Subjects were male carriers of a germline BRCA1/2 mutation enrolled in kConFab with a diagnosis of PC. LOH analysis was performed using multiplex ligation-dependent probe amplification and confirmed using PCR and sequencing. Clinical data was obtained on all individuals together with histopathology review. Results: In total, 134 pedigrees from BRCA1/2 mutation positive families known to include = 1men with PC were reviewed; 192 men were identified as having PC, however, only 26 were found to carry a pathogenic family specific mutation. Of these, 14 were ineligible as prostate tissue was unavailable. LOH was therefore assessed in 12 subjects (3 BRCA1 and 9 BRCA2). LOH at the BRCA2 locus was seen in 8/9 (89%) subjects with a BRCA2 mutation whilst the ninth showed no LOH. None of the samples from BRCA1 carriers were found to have LOH at the BRCA1 locus. For samples showing LOH, sequencing confirmed loss of the wild-type allele. No unique clinical or histopathological subtype was identified. Conclusions: LOH appears to occur very frequently at the BRCA2 locus in PC arising in men known to carry a germline BRCA2 mutation with LOH heavily biased towards loss of the wild-type allele. Whilst the cohort studied is small, these two results strongly indicate that BRCA2 is a tumour suppressor of PC and is the first gene shown to have this property. In contrast, failure to identify LOH in the BRCA1 samples suggests that BRCA1 is unlikely to be integral in the development of PC. These results should be confirmed in a larger cohort and further research into the mechanisms of BRCA2 induced prostate tumorigenesis is warranted. No significant financial relationships to disclose.