Bjarni A. Agnarsson

Genome-wide association study identifies a second prostate cancer susceptibility variant at 8q24

Prostate cancer is the most prevalent noncutaneous cancer in males in developed regions, with African American men having among the highest worldwide incidence and mortality rates. Here we report a second genetic variant in the 8q24 region that, in conjunction with another variant we recently discovered, accounts for about 11%–13% of prostate cancer cases in individuals of European descent and 31% of cases in African Americans. We made the current discovery through a genome-wide association scan of 1,453 affected Icelandic individuals and 3,064 controls using the Illumina HumanHap300 BeadChip followed by four replication studies. A key step in the discovery was the construction of a 14-SNP haplotype that efficiently tags a relatively uncommon (2%–4%) susceptibility variant in individuals of European descent that happens to be very common (∼42%) in African Americans. The newly identified variant shows a stronger association with affected individuals who have an earlier age at diagnosis.

A common variant associated with prostate cancer in European and African populations

With the increasing incidence of prostate cancer, identifying common genetic variants that confer risk of the disease is important. Here we report such a variant on chromosome 8q24, a region initially identified through a study of Icelandic families. Allele −8 of the microsatellite DG8S737 was associated with prostate cancer in three case-control series of European ancestry from Iceland, Sweden and the US. The estimated odds ratio (OR) of the allele is 1.62 (P = 2.7 × 10−11). About 19% of affected men and 13% of the general population carry at least one copy, yielding a population attributable risk (PAR) of ∼8%. The association was also replicated in an African American case-control group with a similar OR, in which 41% of affected individuals and 30% of the population are carriers. This leads to a greater estimated PAR (16%) that may contribute to higher incidence of prostate cancer in African American men than in men of European ancestry.

Two variants on chromosome 17 confer prostate cancer risk, and the one in TCF2 protects against type 2 diabetes

We performed a genome-wide association scan to search for sequence variants conferring risk of prostate cancer using 1,501 Icelandic men with prostate cancer and 11,290 controls. Follow-up studies involving three additional case-control groups replicated an association of two variants on chromosome 17 with the disease. These two variants, 33 Mb apart, fall within a region previously implicated by family-based linkage studies on prostate cancer. The risks conferred by these variants are moderate individually (allele odds ratio of about 1.20), but because they are common, their joint population attributable risk is substantial. One of the variants is in TCF2 (HNF1β), a gene known to be mutated in individuals with maturity-onset diabetes of the young type 5. Results from eight case-control groups, including one West African and one Chinese, demonstrate that this variant confers protection against type 2 diabetes.

Sequence variants at the TERT-CLPTM1L locus associate with many cancer types

The common sequence variants that have recently been associated with cancer risk are particular to a single cancer type or at most two. Following up on our genome-wide scan of basal cell carcinoma, we found that rs401681[C] on chromosome 5p15.33 satisfied our threshold for genome-wide significance (OR = 1.25, P = 3.7 × 10−12). We tested rs401681 for association with 16 additional cancer types in over 30,000 cancer cases and 45,000 controls and found association with lung cancer (OR = 1.15, P = 7.2 × 10−8) and urinary bladder, prostate and cervix cancer (ORs = 1.07−1.31, all P < 4 × 10−4). However, rs401681[C] seems to confer protection against cutaneous melanoma (OR = 0.88, P = 8.0 × 10−4). Notably, most of these cancer types have a strong environmental component to their risk. Investigation of the region led us to rs2736098[A], which showed stronger association with some cancer types. However, neither variant could fully account for the association of the other. rs2736098 corresponds to A305A in the telomerase reverse transcriptase (TERT) protein and rs401681 is in an intron of the CLPTM1L gene.

Common sequence variants on 2p15 and Xp11.22 confer susceptibility to prostate cancer

We conducted a genome-wide SNP association study on prostate cancer on over 23,000 Icelanders, followed by a replication study including over 15,500 individuals from Europe and the United States. Two newly identified variants were shown to be associated with prostate cancer: rs5945572 on Xp11.22 and rs721048 on 2p15 (odds ratios (OR) = 1.23 and 1.15; P = 3.9 × 10−13 and 7.7 × 10−9, respectively). The 2p15 variant shows a significantly stronger association with more aggressive, rather than less aggressive, forms of the disease.

Genome-wide association and replication studies identify four variants associated with prostate cancer susceptibility

We report a prostate cancer genome-wide association follow-on study. We discovered four variants associated with susceptibility to prostate cancer in several European populations: rs10934853[A] (OR = 1.12, P = 2.9 × 10−10) on 3q21.3; two moderately correlated (r2 = 0.07) variants, rs16902094[G] (OR = 1.21, P = 6.2 × 10−15) and rs445114[T] (OR = 1.14, P = 4.7 × 10−10), on 8q24.21; and rs8102476[C] (OR = 1.12, P = 1.6 × 10−11) on 19q13.2. We also refined a previous association signal on 11q13 with the SNP rs11228565[A] (OR = 1.23, P = 6.7 × 10−12). In a multivariate analysis using 22 prostate cancer risk variants typed in the Icelandic population, we estimated that carriers in the top 1.3% of the risk distribution are at a 2.5 times greater risk of developing the disease than members of the general population.

Genomic subtypes of breast cancer identified by array-comparative genomic hybridization display distinct molecular and clinical characteristics

IntroductionBreast cancer is a profoundly heterogeneous disease with respect to biologic and clinical behavior. Gene-expression profiling has been used to dissect this complexity and to stratify tumors into intrinsic gene-expression subtypes, associated with distinct biology, patient outcome, and genomic alterations. Additionally, breast tumors occurring in individuals with germline BRCA1 or BRCA2 mutations typically fall into distinct subtypes.MethodsWe applied global DNA copy number and gene-expression profiling in 359 breast tumors. All tumors were classified according to intrinsic gene-expression subtypes and included cases from genetically predisposed women. The Genomic Identification of Significant Targets in Cancer (GISTIC) algorithm was used to identify significant DNA copy-number aberrations and genomic subgroups of breast cancer.ResultsWe identified 31 genomic regions that were highly amplified in > 1% of the 359 breast tumors. Several amplicons were found to co-occur, the 8p12 and 11q13.3 regions being the most frequent combination besides amplicons on the same chromosomal arm. Unsupervised hierarchical clustering with 133 significant GISTIC regions revealed six genomic subtypes, termed 17q12, basal-complex, luminal-simple, luminal-complex, amplifier, and mixed subtypes. Four of them had striking similarity to intrinsic gene-expression subtypes and showed associations to conventional tumor biomarkers and clinical outcome. However, luminal A-classified tumors were distributed in two main genomic subtypes, luminal-simple and luminal-complex, the former group having a better prognosis, whereas the latter group included also luminal B and the majority of BRCA2-mutated tumors. The basal-complex subtype displayed extensive genomic homogeneity and harbored the majority of BRCA1-mutated tumors. The 17q12 subtype comprised mostly HER2-amplified and HER2-enriched subtype tumors and had the worst prognosis. The amplifier and mixed subtypes contained tumors from all gene-expression subtypes, the former being enriched for 8p12-amplified cases, whereas the mixed subtype included many tumors with predominantly DNA copy-number losses and poor prognosis.ConclusionsGlobal DNA copy-number analysis integrated with gene-expression data can be used to dissect the complexity of breast cancer. This revealed six genomic subtypes with different clinical behavior and a striking concordance to the intrinsic subtypes. These genomic subtypes may prove useful for understanding the mechanisms of tumor development and for prognostic and treatment prediction purposes.

Identification of Subtypes in Human Epidermal Growth Factor Receptor 2–Positive Breast Cancer Reveals a Gene Signature Prognostic of Outcome

PURPOSE Human epidermal growth factor receptor 2 (HER2) gene amplification or protein overexpression (HER2 positivity) defines a clinically challenging subgroup of patients with breast cancer (BC) with variable prognosis and response to therapy. We aimed to investigate the heterogeneous biologic appearance and clinical behavior of HER2-positive tumors using molecular profiling. PATIENTS AND METHODS Hierarchical clustering of gene expression data from 58 HER2-amplified tumors of various stage, histologic grade, and estrogen receptor (ER) status was used to construct a HER2-derived prognostic predictor that was further evaluated in several large independent BC data sets. RESULTS Unsupervised analysis identified three subtypes of HER2-positive tumors with mixed stage, histologic grade, and ER status. One subtype had a significantly worse clinical outcome. A prognostic predictor was created based on differentially expressed genes between the subtype with worse outcome and the other subtypes. The predictor was able to define patient groups with better and worse outcome in HER2-positive BC across multiple independent BC data sets and identify a sizable HER2-positive group with long disease-free survival and low mortality. Significant correlation to prognosis was also observed in basal-like, ER-negative, lymph node-positive, and high-grade tumors, irrespective of HER2 status. The predictor included genes associated with immune response, tumor invasion, and metastasis. CONCLUSION The HER2-derived prognostic predictor provides further insight into the heterogeneous biology of HER2-positive tumors and may become useful for improved selection of patients who need additional treatment with new drugs targeting the HER2 pathway.

A study based on whole-genome sequencing yields a rare variant at 8q24 associated with prostate cancer

In Western countries, prostate cancer is the most prevalent cancer of men and one of the leading causes of cancer-related death in men. Several genome-wide association studies have yielded numerous common variants conferring risk of prostate cancer. Here, we analyzed 32.5 million variants discovered by whole-genome sequencing 1,795 Icelanders. We identified a new low-frequency variant at 8q24 associated with prostate cancer in European populations, rs188140481[A] (odds ratio (OR) = 2.90; Pcombined = 6.2 × 10−34), with an average risk allele frequency in controls of 0.54%. This variant is only very weakly correlated (r2 ≤ 0.06) with previously reported risk variants at 8q24, and its association remains significant after adjustment for all known risk-associated variants. Carriers of rs188140481[A] were diagnosed with prostate cancer 1.26 years younger than non-carriers (P = 0.0059). We also report results for a previously described HOXB13 variant (rs138213197[T]), confirming it as a prostate cancer risk variant in populations from across Europe.

Genetic correction of PSA values using sequence variants associated with PSA levels.

Sequence variants in the human genome are associated with serum levels of prostate-specific antigen. SNPping Away at Prostate Cancer Measuring prostate-specific antigen (PSA) in serum is the only diagnostic test for prostate cancer and is used as a screening tool for deciding whether to perform a biopsy. Yet, this diagnostic test is far from ideal, with more than a third of men with serum PSA levels of 10 ng/ml or greater having no evidence of prostate cancer at biopsy, and some men with very low PSA levels (less than the lower threshold of 2.5 ng/ml), who are not given a biopsy but yet end up having prostate cancer. The lack of specificity and sensitivity of the PSA test and the many confounding factors that influence the test result, including medications, inflammation, and, of course, genotype, have reduced the value of this screening tool. As with most cancers, early detection of prostate cancer leads to a greatly improved chance of survival, so improving the predictive accuracy of this test is of paramount importance. In an effort to investigate whether genome sequence variants can be used to make the PSA test more sensitive, Gudmundsson and colleagues have undertaken a genome-wide association study in 15,757 Icelandic men and 454 British men not yet diagnosed with prostate cancer to see whether they can tie sequence variants [single-nucleotide polymorphisms (SNPs)] to serum PSA levels. The authors identify six loci with SNPs that correlate with PSA levels. They then probed these data more deeply. They looked at these loci in 3834 men who underwent subsequent biopsy of the prostate and demonstrate that three of these loci (10q26, 12q24, and 19q13.33) are associated not only with higher PSA levels but also with a higher probability of a negative biopsy result. The authors suggest that this genotype information should be used to calculate a personalized “cutoff” value for serum PSA levels in each individual to improve the predictive accuracy of the test and to ensure that only men who need a prostate biopsy are subjected to this procedure. Measuring serum levels of the prostate-specific antigen (PSA) is the most common screening method for prostate cancer. However, PSA levels are affected by a number of factors apart from neoplasia. Notably, around 40% of the variability of PSA levels in the general population is accounted for by inherited factors, suggesting that it may be possible to improve both sensitivity and specificity by adjusting test results for genetic effects. To search for sequence variants that associate with PSA levels, we performed a genome-wide association study and follow-up analysis using PSA information from 15,757 Icelandic and 454 British men not diagnosed with prostate cancer. Overall, we detected a genome-wide significant association between PSA levels and single-nucleotide polymorphisms (SNPs) at six loci: 5p15.33 (rs2736098), 10q11 (rs10993994), 10q26 (rs10788160), 12q24 (rs11067228), 17q12 (rs4430796), and 19q13.33 [rs17632542 (KLK3: I179T)], each with Pcombined <3 × 10−10. Among 3834 men who underwent a biopsy of the prostate, the 10q26, 12q24, and 19q13.33 alleles that associate with high PSA levels are associated with higher probability of a negative biopsy (odds ratio between 1.15 and 1.27). Assessment of association between the six loci and prostate cancer risk in 5325 cases and 41,417 controls from Iceland, the Netherlands, Spain, Romania, and the United States showed that the SNPs at 10q26 and 12q24 were exclusively associated with PSA levels, whereas the other four loci also were associated with prostate cancer risk. We propose that a personalized PSA cutoff value, based on genotype, should be used when deciding to perform a prostate biopsy.