Gilles Thomas

A genome-wide association study identifies alleles in FGFR2 associated with risk of sporadic postmenopausal breast cancer

We conducted a genome-wide association study (GWAS) of breast cancer by genotyping 528,173 SNPs in 1,145 postmenopausal women of European ancestry with invasive breast cancer and 1,142 controls. We identified four SNPs in intron 2 of FGFR2 (which encodes a receptor tyrosine kinase and is amplified or overexpressed in some breast cancers) that were highly associated with breast cancer and confirmed this association in 1,776 affected individuals and 2,072 controls from three additional studies. Across the four studies, the association with all four SNPs was highly statistically significant (Ptrend for the most strongly associated SNP (rs1219648) = 1.1 × 10−10; population attributable risk = 16%). Four SNPs at other loci most strongly associated with breast cancer in the initial GWAS were not associated in the replication studies. Our summary results from the GWAS are available online in a form that should speed the identification of additional risk loci.

Replicating genotype-phenotype associations.

What constitutes replication of a genotype–phenotype association, and how best can it be achieved?

Genome-wide association study of prostate cancer identifies a second risk locus at 8q24.

Recently, common variants on human chromosome 8q24 were found to be associated with prostate cancer risk. While conducting a genome-wide association study in the Cancer Genetic Markers of Susceptibility project with 550,000 SNPs in a nested case-control study (1,172 cases and 1,157 controls of European origin), we identified a new association at 8q24 with an independent effect on prostate cancer susceptibility. The most significant signal is 70 kb centromeric to the previously reported SNP, rs1447295, but shows little evidence of linkage disequilibrium with it. A combined analysis with four additional studies (total: 4,296 cases and 4,299 controls) confirms association with prostate cancer for rs6983267 in the centromeric locus (P = 9.42 × 10−13; heterozygote odds ratio (OR): 1.26, 95% confidence interval (c.i.): 1.13–1.41; homozygote OR: 1.58, 95% c.i.: 1.40–1.78). Each SNP remained significant in a joint analysis after adjusting for the other (rs1447295 P = 1.41 × 10−11; rs6983267 P = 6.62 × 10−10). These observations, combined with compelling evidence for a recombination hotspot between the two markers, indicate the presence of at least two independent loci within 8q24 that contribute to prostate cancer in men of European ancestry. We estimate that the population attributable risk of the new locus, marked by rs6983267, is higher than the locus marked by rs1447295 (21% versus 9%).

Mutational processes molding the genomes of 21 breast cancers.

Summary All cancers carry somatic mutations. The patterns of mutation in cancer genomes reflect the DNA damage and repair processes to which cancer cells and their precursors have been exposed. To explore these mechanisms further, we generated catalogs of somatic mutation from 21 breast cancers and applied mathematical methods to extract mutational signatures of the underlying processes. Multiple distinct single- and double-nucleotide substitution signatures were discernible. Cancers with BRCA1 or BRCA2 mutations exhibited a characteristic combination of substitution mutation signatures and a distinctive profile of deletions. Complex relationships between somatic mutation prevalence and transcription were detected. A remarkable phenomenon of localized hypermutation, termed “kataegis,” was observed. Regions of kataegis differed between cancers but usually colocalized with somatic rearrangements. Base substitutions in these regions were almost exclusively of cytosine at TpC dinucleotides. The mechanisms underlying most of these mutational signatures are unknown. However, a role for the APOBEC family of cytidine deaminases is proposed. PaperClip

The Ewing Family of Tumors -- A Subgroup of Small-Round-Cell Tumors Defined by Specific Chimeric Transcripts

BACKGROUND Precise diagnosis of small-round-cell tumors is often a challenge to the pathologist and the clinical oncologist. In Ewings sarcomas and related peripheral primitive neuroectodermal tumors, a t(11;22) translocation or a (21,22) rearrangement is associated with hybrid transcripts of the EWS gene with the FLI1 or ERG gene. To investigate the diagnostic implication of this observation, we searched for these hybrid transcripts in tumors from patients with clinical and radiologic features of Ewings sarcoma or peripheral primitive neuroectodermal tumors. METHODS Samples of RNA from 114 tumors were reverse transcribed and subjected to the polymerase chain reaction with primers designed to amplify the relevant chimeric transcripts. All amplified products were sequenced. RESULTS In-frame hybrid transcripts were observed in 89 cases. A hybrid transcript was found in 83 of 87 cases (95 percent) of Ewings sarcoma or peripheral primitive neuroectodermal tumors. Samples of RNA from all of 12 tumors that had been proved to be other than Ewings sarcoma or neuroectodermal tumors had no hybrid transcript. However, 6 of 15 undifferentiated tumors whose type was ambiguous (nonsecreting, poorly differentiated neuroblastoma or undifferentiated sarcoma) contained a hybrid transcript, suggesting that they might have to be reclassified. CONCLUSIONS A subgroup of small-round-cell tumors identified as belonging to the Ewing family of tumors can be defined according to a specific molecular genetic lesion that is detectable by a rapid, reliable, and efficient method. This approach can be applied to small specimens obtained by fine-needle biopsies.

Multiple loci identified in a genome-wide association study of prostate cancer

We followed our initial genome-wide association study (GWAS) of 527,869 SNPs on 1,172 individuals with prostate cancer and 1,157 controls of European origin—nested in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial prospective study—by testing 26,958 SNPs in four independent studies (total of 3,941 cases and 3,964 controls). In the combined joint analysis, we confirmed three previously reported loci (two independent SNPs at 8q24 and one in HNF1B (formerly known as TCF2 on 17q); P < 10−10). In addition, loci on chromosomes 7, 10 (two loci) and 11 were highly significant (between P < 7.31 × 10−13 and P < 2.14 × 10−6). Loci on chromosome 10 include MSMB, which encodes β-microseminoprotein, a primary constituent of semen and a proposed prostate cancer biomarker, and CTBP2, a gene with antiapoptotic activity; the locus on chromosome 7 is at JAZF1, a transcriptional repressor that is fused by chromosome translocation to SUZ12 in endometrial cancer. Of the nine loci that showed highly suggestive associations (P < 2.5 × 10−5), four best fit a recessive model and included candidate susceptibility genes: CPNE3, IL16 and CDH13. Our findings point to multiple loci with moderate effects associated with susceptibility to prostate cancer that, taken together, in the future may predict high risk in select individuals.

Genome-wide association scan identifies a colorectal cancer susceptibility locus on chromosome 8q24

Using a multistage genetic association approach comprising 7,480 affected individuals and 7,779 controls, we identified markers in chromosomal region 8q24 associated with colorectal cancer. In stage 1, we genotyped 99,632 SNPs in 1,257 affected individuals and 1,336 controls from Ontario. In stages 2–4, we performed serial replication studies using 4,024 affected individuals and 4,042 controls from Seattle, Newfoundland and Scotland. We identified one locus on chromosome 8q24 and another on 9p24 having combined odds ratios (OR) for stages 1–4 of 1.18 (trend; P = 1.41 × 10−8) and 1.14 (trend; P = 1.32 × 10−5), respectively. Additional analyses in 2,199 affected individuals and 2,401 controls from France and Europe supported the association at the 8q24 locus (OR = 1.16, trend; 95% confidence interval (c.i.): 1.07–1.26; P = 5.05 × 10−4). A summary across all seven studies at the 8q24 locus was highly significant (OR = 1.17, c.i.: 1.12–1.23; P = 3.16 × 10−11). This locus has also been implicated in prostate cancer.

A multistage genome-wide association study in breast cancer identifies two new risk alleles at 1p11.2 and 14q24.1 (RAD51L1).

We conducted a three-stage genome-wide association study (GWAS) of breast cancer in 9,770 cases and 10,799 controls in the Cancer Genetic Markers of Susceptibility (CGEMS) initiative. In stage 1, we genotyped 528,173 SNPs in 1,145 cases of invasive breast cancer and 1,142 controls. In stage 2, we analyzed 24,909 top SNPs in 4,547 cases and 4,434 controls. In stage 3, we investigated 21 loci in 4,078 cases and 5,223 controls. Two new loci achieved genome-wide significance. A pericentromeric SNP on chromosome 1p11.2 (rs11249433; P = 6.74 × 10−10 adjusted genotype test, 2 degrees of freedom) resides in a large linkage disequilibrium block neighboring NOTCH2 and FCGR1B; this signal was stronger for estrogen-receptor–positive tumors. A second SNP on chromosome 14q24.1 (rs999737; P = 1.74 × 10−7) localizes to RAD51L1, a gene in the homologous recombination DNA repair pathway. We also confirmed associations with loci on chromosomes 2q35, 5p12, 5q11.2, 8q24, 10q26 and 16q12.1.

Genome-wide association study identifies variants in the ABO locus associated with susceptibility to pancreatic cancer

We conducted a two-stage genome-wide association study of pancreatic cancer, a cancer with one of the lowest survival rates worldwide. We genotyped 558,542 SNPs in 1,896 individuals with pancreatic cancer and 1,939 controls drawn from 12 prospective cohorts plus one hospital-based case-control study. We conducted a combined analysis of these groups plus an additional 2,457 affected individuals and 2,654 controls from eight case-control studies, adjusting for study, sex, ancestry and five principal components. We identified an association between a locus on 9q34 and pancreatic cancer marked by the SNP rs505922 (combined P = 5.37 × 10−8; multiplicative per-allele odds ratio 1.20; 95% confidence interval 1.12–1.28). This SNP maps to the first intron of the ABO blood group gene. Our results are consistent with earlier epidemiologic evidence suggesting that people with blood group O may have a lower risk of pancreatic cancer than those with groups A or B.

Landscape of somatic mutations in 560 breast cancer whole-genome sequences

We analysed whole genome sequences of 560 breast cancers to advance understanding of the driver mutations conferring clonal advantage and the mutational processes generating somatic mutations. 93 protein-coding cancer genes carried likely driver mutations. Some non-coding regions exhibited high mutation frequencies but most have distinctive structural features probably causing elevated mutation rates and do not harbour driver mutations. Mutational signature analysis was extended to genome rearrangements and revealed 12 base substitution and six rearrangement signatures. Three rearrangement signatures, characterised by tandem duplications or deletions, appear associated with defective homologous recombination based DNA repair: one with deficient BRCA1 function; another with deficient BRCA1 or BRCA2 function; the cause of the third is unknown. This analysis of all classes of somatic mutation across exons, introns and intergenic regions highlights the repertoire of cancer genes and mutational processes operative, and progresses towards a comprehensive account of the somatic genetic basis of breast cancer.