Genetic variants in the 8q24 locus and risk of testicular germ cell tumors

An oncofetal and developmental perspective on testicular germ cell cancer

Germ cell tumors (GCTs) represent a diverse group of tumors presumably originating from (early fetal) developing germ cells. Most frequent are the testicular germ cell cancers (TGCC). Overall, TGCC is the most frequent malignancy in Caucasian males (20-40 years) and remains an important cause of (treatment related) mortality in these young men. The strong association between the phenotype of TGCC stem cell components and their totipotent ancestor (fetal primordial germ cell or gonocyte) makes these tumors highly relevant from an onco-fetal point of view. This review subsequently discusses the evidence for the early embryonic origin of TGCCs, followed by an overview of the crucial association between TGCC pathogenesis, genetics, environmental exposure and the (fetal) testicular micro-environment (genvironment). This culminates in an evaluation of three genvironmentally modulated hallmarks of TGCC directly related to the oncofetal pathogenesis of TGCC: (1) maintenance of pluripotency, (2) cell cycle control/cisplatin sensitivity and (3) regulation of proliferation/migration/apoptosis by KIT-KITL mediated receptor tyrosine kinase signaling. Briefly, TGCC exhibit identifiable stem cell components (seminoma and embryonal carcinoma) and progenitors that show large and consistent similarities to primordial/embryonic germ cells, their presumed totipotent cells of origin. TGCC pathogenesis depends crucially on a complex interaction of genetic and (micro-)environmental, i.e. genvironmental risk factors that have only been partly elucidated despite significant effort. TGCC stem cell components also show a high degree of similarity with embryonic stem/germ cells (ES) in the regulation of pluripotency and cell cycle control, directly related to their exquisite sensitivity to DNA damaging agents (e.g. cisplatin). Of note, (ES specific) micro-RNAs play a pivotal role in the crossover between cell cycle control, pluripotency and chemosensitivity. Moreover, multiple consistent observations reported TGCC to be associated with KIT-KITL mediated receptor tyrosine kinase signaling, a pathway crucially implicated in proliferation, migration and survival during embryogenesis including germ cell development. In conclusion, TGCCs are a fascinating model for onco-fetal developmental processes especially with regard to studying cell cycle control, pluripotency maintenance and KIT-KITL signaling. The knowledge presented here contributes to better understanding of the molecular characteristics of TGCC pathogenesis, translating to identification of at risk individuals and enhanced quality of care for TGCC patients (diagnosis, treatment and follow-up).

Genetic variation in AKT1, PTEN and the 8q24 locus, and the risk of testicular germ cell tumor

STUDY QUESTION

Is there an association between testicular germ cell tumor (TGCT) and genetic polymorphisms in AKT1, PTEN and the 8q24 locus?

SUMMARY ANSWER

Our findings suggest that genetic variation in PTEN may influence the risk of TGCT.

WHAT IS KNOWN ALREADY

There is strong evidence that genetic variation influences the risk of TGCT. The oncogene, AKT1, the tumor suppressor gene, PTEN and the chromosome 8q24 locus play important roles in cancer development in general.

STUDY DESIGN, SIZE, DURATION

We have conducted a population-based Norwegian-Swedish case-parent study, based on cases diagnosed in 1990-2008, including 831 triads (TGCT case and both parents), 474 dyads (TGCT case and one parent) and 712 singletons (only the TGCT case). In addition we expanded the study to include 3922 unrelated male controls from the TwinGene project.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We genotyped 26 single nucleotide polymorphisms (SNPs) in AKT1, PTEN and the 8q24 locus. First, triads and dyads were included in a likelihood-based association test. To increase the statistical power, case singletons and controls from the TwinGene project were included in a single test for association. We examined if the allelic effect on TGCT risk differed by histological subgroup, country of origin or parent of origin. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated with Bonferroni correction (P bonf) for multiple testing.

MAIN RESULTS AND THE ROLE OF CHANCE

In the case-parent analyses, none of the 26 SNPs were significantly associated with TGCT. Of the 23 SNPs investigated in the combined study, one SNP in PTEN (rs11202586) remained associated with TGCT risk after adjusting for multiple testing (OR = 1.16, 95% CI = 1.06-1.28, P bonf = 0.040). We found no difference in risk according to histological subgroup, parent of origin or between countries.

LIMITATIONS, REASONS FOR CAUTION

Our study is strengthened by the population-based design and large sample size, which gives high power to detect risk alleles. The reported association was not highly significant, and although it was based on an a priori hypothesis of this tumor suppressor gene being implicated in the etiology of TGCT, replication studies, as well as functional studies of this polymorphism, are warranted.

WIDER IMPLICATIONS OF THE FINDINGS

We report, to our knowledge, a novel association between TGCT and a marker in the tumor suppressor gene PTEN. Previous studies have linked PTEN to TGCT etiology, and there is also a link between PTEN and KITLG, which contains TGCT susceptibility loci revealed through recent genome-wide studies.

Association between total number of deaths, diabetes mellitus, incident cancers, and haplotypes in chromosomal region 8q24 in a prospective study

The 8q24 region is a gene desert, although chromosomal aberrations and somatic amplification involving this region, including translocations involving the protooncogene c-MYC, have been frequently reported in people with cancer. To investigate the role of variants in 8q24 region, the authors analyzed data from a prospective study (n = 10,372 participants who were followed for 11 years) in which a large number of health events (>1,500) occurred (1993-1998). They genotyped all subjects for 5 candidate single nucleotide polymorphisms (rs672888, rs1447295, rs9642880, rs16901979, and rs6983267) that were identified in previous genome-wide scans. Although significant associations with individual single nucleotide polymorphisms were small in magnitude, the authors observed higher increases in the risks of different types of cancer with specific haplotypes, particularly when subjects were homozygous for the haplotype: for breast cancer and homozygotes for haplotype CAGCT, hazard ratio = 3.40, 95% confidence interval: 1.24, 9.21; for prostate cancer and grouped rare haplotypes, hazard ratio = 7.43, 95% confidence interval: 3.00, 18.37; and for brain cancer and homozygotes for haplotype CGGCT, hazard ratio = 13.48, 95% confidence interval: 3.00, 59.53. Significant associations were also observed between haplotypes and deaths from cardiovascular diseases and cerebrovascular diseases; the most stable association was between homozygotes for haplotypes CGTCG and CAGCT and total deaths in men (hazard ratio = 3.5, 95% confidence interval: 1.8, 6.9, and hazard ratio = 2.8, 95% confidence interval: 1.3, 6.4, respectively). In conclusion, the authors have observed a strong pleiotropic effect of the 8q24 region in a large prospective study. This observation can shed light on the mechanisms underlying reported associations between 8q24 variants and disparate chronic diseases.

Invited commentary: more surprises from a gene desert

Pleiotropy across the 8q24 region is perhaps the most intriguing of the genome-wide association findings relating to cancer. This region of chromosome 8 is a gene desert, far from any recognized genes. Guarrera et al., whose work is reported in this issue (Am J Epidemiol. 2012;175(6):479-487), took an epidemiologic approach to learn more about the 8q24 region. They capitalized on their ascertainment of other endpoints in members of the cohort at the Turin site of the European Prospective Investigation Into Cancer and Nutrition to investigate multiple outcomes for additional pleiotropic effects in the 8q24 region. Alternative design options might involve genotyping of more variants, incorporation of more cases, or use of a single control group close to the size of the most common case group. Their analytic methods reflect the uncertainty of the underlying biology. The findings sharpen the scientific question about how variation in the 8q24 region affects pathogenesis. The genome-wide association effort is possible because of the economy of scale afforded by extremely dense genotyping. Strict adherence to the hypothesis-driven approach would ignore information that is obtainable at a trivial cost. The genome-wide association strategy tests whether agnostic data-mining methods can advance knowledge alongside or even in place of the standard hypothesis-driven approach, which is the conventional scientific method children learn in kindergarten and onward, even through graduate school and beyond.

Review: Single nucleotide polymorphisms associated with the oncogenesis of colorectal cancer

Colorectal cancer (CRC) is provoked by interactions between genetic and environmental factors. We herein review the incidence and the mechanisms of action of the reported single nucleotide polymorphisms (SNPs) in the oncogenesis of CRC. More than 15 reports have studied the SNPs at 8q24, which are associated with the incidence of CRC as well as prostate cancer. We have also reported a SNP at the 10p14 locus, and the risks of other loci for CRC oncogenesis. With regard to the underlying mechanism for CRC, 8q24 is a locus of the long-enhancer site for MYC, which could determine the efficacy of MYC transcription. We suggest that 8q24 SNPs might be associated with the progression of CRC cases mediated by MYC expression. In this report, we summarize the published studies of the genetic background SNPs in the oncogenesis of CRC. The level of risk (most studies indicated less than a twofold increase) for CRC was lower than anticipated. Therefore, it is necessary to identify bona fide SNPs that precisely predict the risk for CRC. Alternatively, it is important to consider other factors, such as environmental or lifestyle-related factors, for the future prevention of CRC.

Associations between variants of the 8q24 chromosome and nine smoking-related cancer sites

Recent genome-wide association studies identified key single nucleotide polymorphisms (SNPs) in the 8q24 region to be associated with prostate cancer. 8q24 SNPs have also been associated with colorectal cancer, suggesting that this region may not be specifically associated to just prostate cancer. To date, the association between these polymorphisms and tobacco smoking-related cancer sites remains unknown. Using epidemiologic data and biological samples previously collected in three case-control studies from U.S. and Chinese populations, we selected and genotyped one SNP from each of the three previously determined "regions" within the 8q24 loci, rs1447295 (region 1), rs16901979 (region 2), and rs6983267 (region 3), and examined their association with cancers of the lung, oropharynx, nasopharynx, larynx, esophagus, stomach, liver, bladder, and kidney. We observed noteworthy associations between rs6983267 and upper aerodigestive tract cancers [adjusted odds ratio (ORadj), 1.69; 95% confidence interval (95% CI), 1.28-2.24], particularly in oropharynx (ORadj, 1.80; 95% CI, 1.30-2.49) and larynx (ORadj, 2.04; 95% CI, 1.12-3.72). We also observed a suggestive association between rs6983267 and liver cancer (ORadj, 1.51; 95% CI, 0.99-2.31). When we stratified our analysis by smoking status, rs6983267 was positively associated with lung cancer among ever-smokers (ORadj, 1.45; 95% CI, 1.05-2.00) and inversely associated with bladder cancer among ever-smokers (ORadj, 0.35; 95% CI, 0.14-0.83). Associations were observed between rs16901979 and upper aerodigestive tract cancer among never-smokers and between rs1447295 and liver cancer among ever-smokers. Our results suggest variants of the 8q24 chromosome may play an important role in smoking-related cancer development. Functional and large epidemiologic studies should be conducted to further investigate the association of 8q24 SNPs with smoking-related cancers.

A range of cancers is associated with the rs6983267 marker on chromosome 8

Several genome-wide searches for common cancers have lead to the identification of a small number of loci that harbor low-risk cancer susceptibility markers. One marker, rs6983267 on chromosome 8q24, has been linked to both colon and prostate cancer, and is therefore a good candidate for a multicancer susceptibility marker. To determine the range of cancer sites associated with rs6983267, we genotyped 7,665 cases of cancer, representing 11 common cancer sites, and 1,910 controls. A significant odds ratio (OR) was observed for prostate cancer for carriers of genotype GG [OR, 1.77; 95% confidence interval (CI), 1.47-2.13]. The homozygote OR was higher for tumors with Gleason score 8 to 10 (OR, 1.94; 95% CI, 1.18-3.20) than for tumors with Gleason score 7 and below (OR, 1.65; 95% CI, 1.31-2.08). Significantly elevated (homozygote) ORs were observed for 4 other cancer sites, including colon (OR, 1.36; 95% CI, 1.08-1.72), kidney (OR, 1.52; 95% CI, 1.12-2.05), thyroid (OR, 1.37; 95% CI, 1.02-1.82), and larynx (OR, 1.39; 95% CI, 1.02-1.90). Information was available on family histories of cancer for eight sites. For six of the eight sites (prostate, breast, bladder, larynx, lung, and kidney), the homozygote ORs were higher for cases with a positive family history (at least one first-degree with any cancer) than for cases with unaffected first-degree relatives. Our results suggest that the range of cancers associated with the rs6983267 marker might be larger than previously thought.