Genetic analysis of families with nonsmoking lung cancer probands

Tobacco, Genetic Susceptibility and Lung cancer

Exposure to tobacco smoke is an established risk factor for lung cancer, although a possible role for genetic susceptibility in the development of lung cancer has been inferred from familial clustering of the disease and segregation analysis. Findings of familial aggregation and statistical evidence for a major susceptibility gene have led to the search for high penetrant, rare, single genes and low penetrant, high frequency susceptibility genes for lung cancer. The relatively small number of linkage studies conducted to date, have identified potential lung cancer susceptibility loci on chromosomes 6q, 12p, and 19q. A variety of studies have examined single nucleotide polymorphisms of several low penetrant, high frequency genes encoding for enzymes involved in the metabolism of carcinogens and DNA damage repair, as likely candidate susceptibility genes. These studies have produced somewhat conflicting findings and, when significant, only modest associations have been reported. Relatively few studies have looked for potential gene-environment interactions, explored associations between two or more genetic polymorphisms or evaluated interactions between genetic polymorphisms and endogenous risk factors. Few large scale genome wide association studies conducted recently have provided evidence that common variation on chromosome 15q25.1, 5p15.33 and 6p21.33 influences lung cancer risk and cancer types with strong environmental risk factors. It is hoped that newer research strategies, selecting candidate genes within pathways and genotype at multiple markers within a gene, employing new technologies, may allow complete coverage of the variation within candidate genes in multiple pathways and to unravel the genetic susceptibility to lung cancer. This knowledge could, in turn, be used to identify persons at risk, to individualize treatments such as chemoprevention, to personalize harms of smoking and to motivate cessation.

Matrix metalloproteinase 1 (MMP1) is associated with early-onset lung cancer

Matrix metalloproteinases (MMP) play a key role in the breakdown of extracellular matrix and in inflammatory processes. MMP1 is the most highly expressed interstitial collagenase degrading fibrillar collagens. Overexpression of MMP1 has been shown in tumor tissues and has been suggested to be associated with tumor invasion and metastasis. Nine haplotype tagging and additional two intronic single nucleotide polymorphisms (SNP) of MMP1 were genotyped in a case control sample, consisting of 635 lung cancer cases with onset of disease below 51 years of age and 1,300 age- and sex-matched cancer-free controls. Two regions of linkage disequilibrium (LD) of MMP1 could be observed: a region of low LD comprising the 5' region including the promoter and a region of high LD starting from exon 1 to the end of the gene and including the 3' flanking region. Several SNPs were identified to be individually significantly associated with risk of early-onset lung cancer. The most significant effect was seen for rs1938901 (P = 0.0089), rs193008 (P = 0.0108), and rs996999 (P = 0.0459). For rs996999, significance vanished after correction for multiple testing. For each of these SNPs, the major allele was associated with an increase in risk with an odds ratio between 1.2 and 1.3 (95% confidence interval, 1.0-1.5). The haplotype analysis supported these findings, especially for subgroups with high smoking intensity. In summary, we identified MMP1 to be associated with an increased risk for lung cancer, which was modified by smoking.

Genetic variants in cell cycle control pathway confer susceptibility to lung cancer

PURPOSE

To test the hypothesis that common sequence variants of cell cycle control genes may affect lung cancer predisposition.

EXPERIMENTAL DESIGN

We explored lung cancer risk associations of 11 polymorphisms in seven cell cycle genes in a large case-control study including 1,518 Caucasian lung cancer patients and 1,518 controls.

RESULTS

When individuals with variant-containing genotypes were compared with homozygous wild-type carriers, a significantly increased lung cancer risk was identified for polymorphisms in p53 intron 6 [rs1625895; odds ratio (OR), 1.29; 95% confidence interval (95% CI), 1.08-1.55] and in p27 5' untranslated region (UTR; rs34330; OR, 1.27; 95% CI, 1.01-1.60). Compared with homozygous wild-types, the homozygous variant genotypes of STK15 F31I and CCND1 G870A were associated with a significantly altered lung cancer risk with ORs of 0.58 (95% CI, 0.37-0.90) and 1.26 (95% CI, 1.03-1.53), respectively. To assess the cumulative effects of all the investigated polymorphisms on lung carcinogenesis, we conducted a combined analysis and found that compared with low-risk individuals with few adverse alleles, individuals with more adverse alleles had an increased risk in a significant dose-dependent manner (P(trend) = 0.041). This pattern was more evident in ever smokers (P(trend) = 0.037), heavy smokers (P(trend) = 0.020), and older subjects (P(trend) = 0.011). Higher-order gene-gene interactions were evaluated using the classification and regression tree analysis, which indicated that STK15 F31I and p53 intron 6 polymorphisms might be associated with lung carcinogenesis in never/light-smokers and heavy smokers, respectively.

CONCLUSIONS

Our results suggest that cell cycle gene polymorphisms and smoking may function collectively to modulate the risk of lung cancer.

Seizure 6-Like (SEZ6L) Gene and Risk for Lung Cancer

DNA pooling in combination with high-throughput sequencing was done as a part of the Sequenom-Genefinder project. In the pilot study, we tested 83,715 single nucleotide polymorphisms (SNP), located primarily in gene-based regions, to identify polymorphic susceptibility variants for lung cancer. For this pilot study, 369 male cases and 287 controls of both sexes (white Europeans of Southern German origin) were analyzed. The study identified a candidate region in 22q12.2 that contained numerous SNPs showing significant case-control differences and that coincides with a region that was shown previously to be frequently deleted in lung cancer cell lines. The candidate region overlies the seizure 6-like (SEZ6L) gene. The pilot study identified a polymorphic Met430Ile substitution in the SEZ6L gene (SNP rs663048) as the top candidate for a variant modulating risk of lung cancer. Two replication studies were conducted to assess the association of SNP rs663048 with lung cancer risk. The M. D. Anderson Cancer Center study included 289 cases and 291 controls matched for gender, age, and smoking status. The Liverpool Lung Project (a United Kingdom study) included 248 cases and 233 controls. Both replication studies showed an association of the rs663048 with lung cancer risk. The homozygotes for the variant allele had more than a 3-fold risk compared with the wild-type homozygotes [combined odds ratio (OR), 3.32; 95% confidence interval (95% CI), 1.81-7.21]. Heterozygotes also had a significantly elevated risk of lung cancer from the combined replication studies with an OR of 1.15 (95% CI, 1.04-1.59). The effect remained significant after adjusting for age, gender, and pack-years of tobacco smoke. We also compared expression of SEZ6L in normal human bronchial epithelial cells (n = 7), non-small cell lung cancer (NSCLC; n = 52), and small cell lung cancer (SCLC; n = 22) cell lines by using Affymetrix HG-U133A and HG-U133B GeneChips. We found that the average expression level of SEZ6L in NSCLC cell lines was almost two times higher and in SCLC cell lines more than six times higher when compared with normal lung epithelial cell lines. Using the National Center for Biotechnology Information Gene Expression Omnibus database, we found a approximately 2-fold elevated and statistically significant (P = 0.004) level of SEZ6L expression in tumor samples compared with normal lung tissues. In conclusion, the results of these studies representing 906 cases compared with 811 controls indicate a role of the SEZ6L Met430Ile polymorphic variant in increasing lung cancer risk.

Familial multiple primary lung cancers: a population-based analysis from Sweden

Multiple primary cancers arise because of inherited or acquired deficiencies, and their causes may depend on the first primary cancer, or they may be entirely independent. We used a nation-wide family dataset to search for evidence for a genetic predisposition to lung cancer. The Swedish Family-Cancer Database includes all Swedes born in 1932 and later with their parents, totalling over 10.2 million individuals. Cancer cases were retrieved from the Swedish Cancer Registry up to year 2000. Standardized incidence ratios (SIR) and 95% confidence limits (CI) were calculated for first and second primary lung cancers by a family history. The incidence of second primary lung cancer was nine times higher among cases with familial lung cancer compare to that of first primary lung cancer. The proportion of multiple primary lung cancer patients with family history for lung cancer was 4.7% (9/190) for men and 6.5% (5/77) for women. Lung cancer patients with a family history of lung cancer were at a significantly increased risk for subsequent primary lung cancer among both men (SIR=9.89, 95%CI 4.48-18.66) and women (SIR=17.86, 95%CI 5.63-42.00). The corresponding SIRs in patients without a family history were 2.04 (95%CI 1.75-2.36) and 5.10 (95%CI 3.99-6.43) for men and women, respectively. The present study suggests that the development from the first primary lung cancer to the second primary lung cancer may be more strongly affected by genetic factor than the first primary lung cancer.

Inherited predisposition to early onset lung cancer according to histological type

The role of hereditary factors in lung cancer is less well understood than in many other human neoplastic diseases. We used a nation-wide family dataset to search for evidence for a genetic predisposition in lung cancer. The Swedish Family-Cancer Database includes all Swedes born in 1932 and later (0- to 68-year-old offspring) with their parents, totaling over 10.2 million individuals. Cancer cases were retrieved from the Swedish Cancer Registry up to year 2000. Standardized incidence ratios (SIR) and 95% confidence limits (CI) were calculated for age-specific familial risks in offspring by parental or sibling proband, separately. A Kappa test was used to examine the association between familial risk and histology. Compared to the rate of lung cancers among persons without family history, a high risk by parental family history in adenocarcinoma (2.03) and large cell carcinoma (2.14) was found, and only a slightly lower risk was found among patients with squamous cell carcinoma (1.63) and small cell carcinoma (1.55). Among siblings, an increased risk was shown for concordant adenocarcinoma and small cell carcinoma at all ages and for all histological types when cancer was diagnosed before age 50. At young age, risks between siblings were higher than those between offspring and parents. The present data suggest that a large proportion of lung cancers before age 50 years appears to be heritable and probably due to a high-penetrant recessive gene or genes that predispose to tobacco carcinogens; however, this hypothesis needs to be tested in segregation analysis with a large number of pedigrees.

Complex segregation analysis reveals a multigene model for lung cancer

Lung cancer risk is largely attributed to tobacco exposure, but genetic predisposition also plays an etiologic role. Several studies have investigated the involvement of genetic predisposition in lung cancer aggregation in affected families, although with inconsistent results. Some studies have provided evidence for Mendelian inheritance, whereas others have suggested that environmental models are most appropriate for lung cancer aggregation in families. To examine the genetic basis of lung cancer, we performed segregation analysis on 14,378 individuals from 1,561 lung cancer case families, allowing for the effects of smoking, sex, and age. Both a Mendelian decreasing model and a Mendelian codominant model were found to be the best fitting models for susceptibility. However, when we modeled age-of-onset, all Mendelian models and the environmental model were rejected suggesting that multiple genetic factors (possibly multiple genetic loci and interactions) contribute to the age-of-onset of lung cancer. The results provide evidence that multiple genetic factors contribute to lung cancer and may act as a guide in further studies to localize susceptibility genes in lung cancer.

Lung adenocarcinoma and human papillomavirus infection

Over the past three decades, the incidence of lung adenocarcinoma has increased worldwide. Most individuals with lung adenocarcinoma (especially women) are nonsmokers. Reported risk factors for the development of lung adenocarcinoma include cigarette smoking; exposure to cooking fumes, air pollution, second-hand smoke, asbestos, and radon; nutritional status; genetic susceptibility; immunologic dysfunction; tuberculosis infection; and asthma. Human papillomavirus (HPV) infection is a known risk factor for the development of squamous cell carcinoma (SCC), but it has not been thoroughly assessed as a potential risk factor for the development of pulmonary adenocarcinoma. More than 50% of people are infected with HPV during their lifetimes, either via intrauterine or postnatal infection. Recent studies involving Taiwanese patients have demonstrated a possible association between HPV infection and the risk of developing pulmonary adenocarcinoma. HPV transmission pathways have not yet been conclusively identified. The observation of certain types of HPV in association with cervical and oral SCC raises the possibility of sexual transmission of HPV from the cervix to the oral cavity, with subsequent transmission to the larynx and then to the lung. HPV infection and metaplasia in lung tissue may increase an individual's susceptibility to the tumorigenesis of pulmonary adenocarcinoma. Further epidemiologic and pathologic investigations will be necessary to establish a causal relation.

Familial cancer aggregation and the risk of lung cancer

CONTEXT

Around 90% of lung cancer worldwide is attributable to cigarette smoking, although less than 20% of cigarette smokers develop lung cancer. Other factors such as diet, chronic lung diseases, occupation and possibly environmental agents also contribute to this cancer. Genetic factors seem to play a role in lung cancer, but the precise characteristics influencing lung cancer susceptibility are not known, since genetic factors are easily obscured by the strong environmental determinants of lung cancer, particularly smoking.

OBJECTIVE

To estimate the effect that cancer occurrence among first-degree relatives has on the risk of lung cancer.

DESIGN

Hospital-based case-control study.

SETTING

The metropolitan region of São Paulo, Brazil.

PARTICIPANTS

334 incident lung cancer cases and 578 controls matched by hospitals.

MAIN MEASUREMENTS

By means of a structured questionnaire, cases and controls were interviewed about cancer occurrence in first-degree relatives, tobacco smoking, exposure to passive smoking, occupation, migration and socioeconomic status. Non-conditional logistic regression was used to calculate the risk of familial cancer aggregation, the effect of cancer in first-degree relatives and smoking in conjunction, and for controlling confounders.

RESULTS

The adjusted odds ratio (OR) revealed a slight, but not statistically significant, excess risk of lung cancer for subjects with a history of lung cancer in relatives (OR 1.21; 95% confidence interval [CI] 0.50 - 2.92). The same was found among those with a history of other tobacco-related cancers in relatives (OR 1.36; 95% CI 0.87 - 2.14). A step gradient effect was observed regarding lung cancer risk, in accordance with increases in the number of pack-years of cigarette consumption. An interaction between familial cancer aggregation and tobacco smoking was detected.

CONCLUSIONS

A mildly elevated risk of lung cancer among persons with a positive history of lung and other tobacco-related cancers was observed. The finding of an interaction between the variables of familial cancer aggregation and smoking suggests that familial cancer aggregation could be considered as a marker of susceptibility, increasing the risk of lung cancer among smokers. These results improve our knowledge of lung carcinogenesis and can guide future cancer genetic studies.

Lung cancer risk in families of nonsmoking probands: heterogeneity by age at diagnosis

In an earlier investigation, we did not detect a major genetic component to lung cancer in families of nonsmoking lung cancer probands. However, heterogeneity with respect to familial aggregation, based on probands' age at diagnosis, was evident. We reanalyzed our previously collected data of 257 families, stratified by age at diagnosis of the probands, using complex segregation analysis. We specifically tested the effects of a Mendelian diallelic gene, history of tobacco use, and history of selected chronic lung diseases in families with a proband diagnosed at the age of 60 years or older and in families with a younger proband (i.e. , under 60 years of age). Cases were identified from the Metropolitan Detroit Cancer Surveillance System. Information on lung cancer occurrence, smoking history, and chronic respiratory diseases in first-degree relatives was obtained for 210 older probands and for 47 younger probands. In older probands' families, no evidence of a major genetic effect was detected. A history of emphysema and tobacco-smoke exposure were found to be significant risk factors. In younger probands' families, a Mendelian codominant model with significant modifying effects of smoking and chronic bronchitis best explained the observed data. Our results suggest the presence of a high-risk gene contributing to early-onset lung cancer in a population where the probands are nonsmokers.

Is there a genetic basis for lung cancer susceptibility?

The major risk factor for lung cancer is exposure to tobacco smoke. Exposure to radon, heavy metals used in smelting, and asbestos also greatly increase risks for lung cancer. However, only about 11% of tobacco smokers ultimately develop lung cancer, suggesting that genetic factors may influence the risk for lung cancer among those who are exposed to carcinogens. Further support for this hypothesis is provided by several epidemiological studies and also from molecular epidemiological studies. Epidemiological studies show approximately 14-fold increased risks for lung cancer among average tobacco smokers and approximately 2.5-fold increased risks attributable to a family history of lung cancer after controlling for tobacco smoke. Segregation analyses suggest that a rare autosomal dominant gene may explain susceptibility to early-onset lung cancer, but these results explain a minority of lung cancer cases, which include a family history. Therefore, more common genetic variants or polymorphisms are hypothesized to affect lung cancer risk. Environmental carcinogenesis resulting from tobacco smoke exposure is a complex process that can involve activation of procarcinogens that lead to adduct formation and subsequent failure of DNA repair, which should normally remove these adducts. Studies comparing DNA repair capacity among newly diagnosed lung cancer patients and age-matched controls indicate significant differences between the two groups. On culturing with bleomycin lymphocytes from lung cancer patients and age- and ethnicity-matched controls, the lymphocytes from lung cancer cases have been consistently observed to show higher levels of chromatid breaks than the control lymphocytes. A similar assay has been developed using benzo-[alpha]pyrene diol-epoxide (BPDE), a reactive substrate that is derived by in vitro processes from benzo[alpha]pyrene, a major carcinogen in tobacco smoke. Results from this assay show an even more significantly higher level of damaged chromatids in lung cancer patients than in controls. Poor DNA repair is independent of tobacco smoking status. The cellular processes involved in DNA repair of bleomycin and BPDE have not yet been fully elaborated. However, the consistency of findings with these two carcinogens indicates that DNA repair capacity influences risk for lung cancer among individuals.