Prevalence of BRCA mutations among women with triple-negative breast cancer (TNBC) in a genetic counseling cohort.

BACKGROUND: Revised NCCN guidelines recommend that women ≤60 years with triple-negative breast cancer (TNBC) be referred for consideration of genetic counseling. Small, homogeneous samples have limited evaluation of BRCA mutation prevalence among different ethnicities affected by TNBC subtype. We sought to determine whether the prevalence of BRCA mutations within a TNBC cohort differs by demographic factors. METHODS: We performed a retrospective review of patients with TNBC referred for genetic counseling at two academic Hereditary Cancer Clinics between 2000 and 2012. Demographic data were collected, including age at diagnosis and race/ethnicity. Race was categorized as African American (AA), Ashkenazi Jewish (AJ), Asian, Caucasian, Hispanic, or other. Primary outcome was BRCA mutation status, analyzed by race/ethnicity and age at diagnosis. RESULTS: A total of 469 patients with TNBC who underwent testing for BRCA genetic mutations were identified, of which 450 patients had evaluable BRCA testing results; 139 (30.8 %) had confirmed BRCA1 (n = 106) or BRCA2 (n = 32) mutations. BRCA mutation prevalence differed by ethnicity and race: AA (20.4 %), AJ (50 %), Asian (28.5 %), Caucasian (33.3 %), and Hispanic (20 %). The prevalence of genetic mutations also differed by age at diagnosis: <40 years (43.8 %), 40-49 years (27.4 %), 50-59 years (25.3 %), 60-69 years (12.5 %), and >70 years (16.6 %). CONCLUSIONS: The prevalence of genetic mutations among women with TNBC referred for genetic counseling is high and differs significantly by ethnicity/race and age. This data helps to refine mutation risk estimates among women with TNBC, allowing for more personalized genetic counseling potentially aiding in improved patient decision-making.

Individual variability in the detoxification of carcinogenic arylhydroxylamines in human breast.

Cytochrome b(5) (b5) and NADH cytochrome b(5) reductase (b5R) detoxify reactive hydroxylamine (NHOH) metabolites of known arylamine and heterocyclic amine mammary carcinogens. The aim of this study was to determine whether NHOH reduction for the prototypic arylamine 4-aminobiphenyl (4-ABP) was present in human breast and to determine whether variability in activity was associated with single nucleotide polymorphisms (SNPs) in the coding, promoter, and 3'untranslated region (UTR) regions of the genes encoding b5 (CYB5A) and b5R (CYB5R3). 4-ABP-NHOH reduction was readily detected in pooled human breast microsomes, with a K(m) (280µM) similar to that found with recombinant b5 and b5R, and a V(max) of 1.12 ± 0.19 nmol/min/mg protein 4-ABP-NHOH reduction varied 75-fold across 70 individual breast samples and correlated significantly with both b5 (80-fold variability) and b5R (14-fold) immunoreactive protein. In addition, wide variability in b5 protein expression was significantly associated with variability in CYB5A transcript levels, with a trend toward the same association between b5R and CYB5R3. Although a sample with a novel coding SNP in CYB5A, His22Arg, was found with low reduction and b5 expression, no other SNPs in either gene were associated with outlier activity or protein expression. We conclude that b5 and b5R catalyze the reduction of 4-ABP-NHOH in breast tissue, with very low activity, protein, and messenger RNA expression in some samples, which cannot be attributed to promoter, coding, or 3'UTR SNPs. Further studies are underway to characterize the transcriptional regulation of CYB5A and CYB5R3 and begin to understand the mechanisms of individual variability in this detoxification pathway.