Prevalence and predictors of BRCA1 and BRCA2 mutations in a population-based study of breast cancer in white and black American women ages 35 to 64 years

Breast cancer risk associated with BRCA1 and BRCA2 in diverse populations

Germline mutations in the BRCA1 or BRCA2 tumour-suppressor genes are strong predictors of breast and/or ovarian cancer development. The contribution of these mutations to breast cancer risk within any specific population is a function of both their prevalence and their penetrance. Mutation prevalence varies among ethnic groups and may be influenced by founder mutations. Penetrance can be influenced by mutation-specific phenotypes and the potential modifying effects of the patient's own genetic and environmental background. Although estimates of both mutation prevalence and mutation penetrance rates are inconsistent and occasionally controversial, understanding them is crucial for providing accurate risk information to each patient.

How growth hormone may be linked to cancer: concerns and perspective

Recent evidence from epidemiology indicates that inter-individual variations in the growth hormone (GH)/IGF-I pathway affect the risk of individuals developing common epithelial cancers. This is supported by associations between normal common variants within genes from the pathway and these cancers, which excludes many potential confounding issues, such as reverse causality. This raises concern for the increasing numbers of patients treated with GH; although replacement therapy for GH-deficiency should aim to restore normality, which should then only incur a normal risk. The links with cancer also offers promising new opportunities. Clinical trials treating cancer patients with pharmaceuticals targeting the IGF-I receptor are well advanced with promising initial findings. In the future, there has to be much more emphasis within oncology on prevention and the GH/IGF-I pathway is one of few identified risk factors that are modifiable, not just by pharmaceutical, but also nutritional, interventions that may, in the long term, be more appropriate. Assessing the status of the GH/IGF-I pathway in individuals may also provide a means for targeting screening programs and preventative measures.

Gene expression assays

The study of the profile of gene expression in a cell or tissue at a particular moment gives an insight into the plans of the cell for protein synthesis. Recent technological advances make it possible to analyze the expression of the entire genome in a single experiment. These "gene expression assays" complement or replace previous assays which measured the gene expression of only one gene, or a select group of genes. Within this chapter we outline the development of the gene expression assay and provide examples of the wide range of disciplines in which it is used. An overview of the current technologies is given, and includes an introduction to laser capture microdissection and linear amplification of RNA, both of which have extended the application of gene expression assays. Illustrative examples in the field of cancer and neuroscience highlight the scientific achievements. This technology has made in understanding the pathogenesis of diseases, including breast cancer, Huntington's disease, and schizophrenia. With recent advances including exon arrays to investigate alternative splicing, tiling arrays to investigate novel transcription start sites, and on-chip chromatin immunoprecipitation to investigate DNA-protein interactions, the future of gene expression assays is set to further our understanding of the complexities of gene expression.

Rare germline mutations in the BRCA2 gene are associated with early-onset prostate cancer

Studies of families who segregate BRCA2 mutations have found that men who carry disease-associated mutations have an increased risk of prostate cancer, particularly early-onset disease. A study of sporadic prostate cancer in the UK reported a prevalence of 2.3% for protein-truncating BRCA2 mutations among patients diagnosed at ages ⩽55 years, highlighting the potential importance of this gene in prostate cancer susceptibility. To examine the role of protein-truncating BRCA2 mutations in relation to early-onset prostate cancer in a US population, 290 population-based patients from King County, Washington, diagnosed at ages <55 years were screened for germline BRCA2 mutations. The coding regions, intron–exon boundaries, and potential regulatory elements of the BRCA2 gene were sequenced. Two distinct protein-truncating BRCA2 mutations were identified in exon 11 in two patients. Both cases were Caucasian, yielding a mutation prevalence of 0.78% (95% confidence interval (95%CI) 0.09–2.81%) and a relative risk (RR) of 7.8 (95%CI 1.8–9.4) for early-onset prostate cancer in white men carrying a protein-truncating BRCA2 mutation. Results suggest that protein-truncating BRCA2 mutations confer an elevated RR of early-onset prostate cancer. However, we estimate that <1% of early-onset prostate cancers in the general US Caucasian population can be attributed to these rare disease-associated BRCA2 mutations.

Breast cancer: a candidate gene approach across the estrogen metabolic pathway

Polymorphisms within the estrogen metabolic pathway are prime candidates for a possible association with breast cancer risk. We investigated 11 genes encoding key proteins of this pathway for their potential contribution to breast cancer risk. Of these CYP17A1, CYP19A1, EPHX1, HSD17B1, SRD5A2, and PPARG2 participate in biosynthesis, CYP1A1, CYP1B1, COMT, GSTP1, and SOD2 in catabolism and detoxification. We performed a population-based case-control study with 688 incident breast cancer cases and 724 controls from Germany and genotyped 18 polymorphisms by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), PCR based RFLP (restriction fragment length polymorphism), and TaqMan allelic discrimination. Genotype frequencies were compared between cases and controls and odds ratios were calculated by conditional logistic regression. Further statistical analyses were based on cluster analysis, multifactor dimensionality reduction, logic regression, and global testing. Single factor analyses pointed to CYP1B1_1294_GG as a possible breast cancer risk modulator (OR = 2.57; 95% CI: 1.34-4.93) and two way stratification suggested associations between BMI > or = 30 kg/m(2) and COMT_472_GG (P = 0.0076 and P = 0.0026), BMI < 20 kg/m(2) and HSD17B1_937_GG (P = 0.0082) as well as CYP17A1_-34_CC and HRT use > or =10 years (P = 0.0063). Following correction for multiple testing none of these associations remained significant. No significant association between breast cancer risk and genetic polymorphisms was observed in multifactor analyses. The tested polymorphisms of the estrogen metabolic pathway may not play a direct role in breast cancer risk. Therefore, future association studies should be extended to other polymorphisms and other regulatory pathways.

The prevalence of BRCA2 mutations in familial pancreatic cancer

Mutations in the BRCA2 gene have been implicated in pancreatic cancer susceptibility through studies of high-risk breast and ovarian cancer families. To determine the contribution of mutations in BRCA2 to familial pancreatic cancer, we screened affected probands from 151 high-risk families identified through pancreatic cancer clinics for germ-line BRCA2 mutations. Of these families, 118 had two or more first- and second-degree relatives with pancreatic cancer, and an additional 33 had two or more affected second-degree relatives. The average age of onset for pancreatic cancer was 62.8 years. Five BRCA2 truncating mutations were identified, three in families with two or more first- and second-degree relatives with pancreatic cancer. Three of the families with mutations had a history of breast cancer but not ovarian cancer. Four of five families with mutations were identified through probands with early-onset (<55 years) pancreatic cancer. The results of this study were combined with those from a BRCA2 mutation study of 29 other families from the same Johns Hopkins University National Familial Pancreatic Tumor Registry to estimate the frequency of BRCA2 mutations. A total of 10 carriers from 180 families were identified, suggesting that BRCA2 mutations account for 6% of moderate and high-risk pancreatic cancer families.

Ovarian Cancer Risk and Polymorphisms Involved in Estrogen Catabolism

Polymorphisms within genes responsible for estrogen catabolism could alter cellular levels of genotoxic 4-hydroxylated catechol estrogens and antiangiogenic 2-methoxyestradiol, thus influencing risk of developing ovarian cancer. We carried out a population-based case-control study of 310 epithelial ovarian cancer cases and 585 controls in African-American and Caucasian women ages 35 to 54 years from Seattle, Atlanta, and Detroit metropolitan areas. Subjects were interviewed and genotyped for CYP1A1 m1, m2, m3, and m4; CYP1B1 Arg(48)Gly, Ala(119)Ser, Val(432)Leu, and Asn(453)Ser; COMT Val(158)Met; UGT1A1 A(TA)nTAA; and SULT1A1 Arg(213)His polymorphisms. Unconditional logistic regression was used to calculate odds ratios (OR). Haplotypes were inferred and analyzed using models based on expectation-maximization with progressive ligation and Bayesian coalescence theory. CYP1B1 Leu(432) carriers were at increased risk of ovarian cancer, with an adjusted OR of 1.5 (95% confidence interval, 1.1-2.3) compared with Val(432) homozygotes. The most common CYP1B1 haplotype was Arg(48)-Ala(119)-Val(432)-Asn(453). All other haplotypes with frequencies >5% contained the Leu(432) allele. In diplotype analyses, relative to women homozygous for Arg(48)-Ala(119)-Val(432)-Asn(453), women with diplotypes containing at least one Leu(432) allele had adjusted ORs ranging from 1.3 to 2.2. Among women homozygous for COMT Met(158), carriers of CYP1B1 Leu(432) had a 2.6-fold increase in risk relative to CYP1B1 Val(432) homozygotes (95% confidence interval, 1.1-5.9). This latter result is opposite in direction from a similar analysis conducted by other investigators in a different study population. No association of ovarian cancer risk was observed with any of the other polymorphisms examined, either alone or in combination.