Lung cancer is the leading cause of cancer incidence and death worldwide. Once diagnosed with lung cancer, only 15% of individuals survive longer than five years. Tobacco-smoking is estimated to be responsible for 85- 90% of lung cancer cases, but fewer than 20% of smokers develop lung cancer, suggesting that other factors may play a predisposing role. Recently, several large-scale genome-wide association studies have reported that SNPs in the telomerase reverse transcriptase (TERT) gene are strongly associated with lung cancer risk. TERT is a telomere maintenance gene, and is often a site of chromosomal abnormalities in lung tumors. Telomeres, located at the ends of chromosomes, protect the genetic integrity of cells. They progressively shorten with every cell division, and after they reach a critically short length, the cell will undergo apoptosis or cellular senescence. Alternatively, critically short telomeres can cause chromosomal instability and fusions, allowing the accumulation of genetic changes in favor of carcinogenesis. While three case-control studies have observed that shorter telomere length was associated with lung cancer risk, longer telomere length (measured prior to lung cancer diagnosis) was associated with increased lung cancer risk in a nested case- control study. Given the discrepant but suggestive findings from these four studies, additional studies are needed to elucidate the role of telomere length in lung cancer development. It is possible that shortening of specific chromosomes is associated with an increased risk of lung cancer, though this has not been studied previously. Also, no studies to date have examined lymphocyte telomere length and lung cancer survival. In a nested case-control study (n=790 cases, 1,558 controls) within the Carotene and Retinol Efficacy Trial, a cohort of heavy smokers with blood samples collected prospectively, we propose to examine: whether global, and chromosome-arm-specific, telomere length measured in samples collected prior to lung cancer diagnosis are associated with lung cancer risk;whether approximately 400 tag and putative functional SNPs in TERT and other telomere maintenance-related genes are associated with lung cancer risk;and whether telomere length and variation in telomere maintenance genes are associated with survival among individuals who develop lung cancer. A large, prospective study among smokers such as the one proposed will provide evidence that will aid in clarifying whether telomere length is associated with lung cancer risk and/or survival. If either global or chromosome-specific telomere length is associated with lung cancer risk, this measurement could possibly be developed to identify a subset of individuals at particularly high risk of lung cancer, among the high-risk population of smokers.
Telomeres are chromatin-protein complexes that cap chromosome ends and protect chromosomes from degradation and fusion with one another. As telomeres shorten, their ability to protect the chromosome diminishes. In this study, we will examine whether short telomere length, and variation in genes regulating telomere length, are associated with lung cancer risk and survival.
