Abstract 2251: Alu retroelement copy number, leukocyte telomere length, and lung cancer risk in the prospective Prostate, Lung, Colorectal and Ovarian Cancer (PLCO) Screening Trial
Authors: Wong Jason Yat-Yang , Cawthon Richard , Hu Wei , Ezennia Somayina , Gadalla Shahinaz , Breeze Charles , Blechter Batel , Freedman Neal , Huang Wen-Yi , Hosgood H. Dean , Seow Wei Jie , Bassig Bryan , Rahman Mohammad , Hayes Richard , Rothman Nathaniel , Lan Qing 
Published: June 2022

Abstract
Prospective cohort and genome-wide association studies have found consistent associations between longer leukocyte telomere length (LTL) and increased lung cancer risk. These findings present a paradox in the traditional expectations of telomere dynamics in cancer development, as longer telomeres are generally considered to be reflective of less advanced age and greater genomic stability. We posited that longer LTL may reflect or lead to delayed cellular senescence allowing cells to accumulate genomic abnormalities that drive lung carcinogenesis. Furthermore, increased copy number of Alu retroelements, repetitive mobile DNA sequences that are approximately 300 base pairs in length, could also reflect genomic instability. We previously found that exposure to diesel exhaust, a known lung carcinogen, was associated with increased Alu copy number and suspect that increased Alu retrotransposition could influence lung carcinogenesis. However, the interrelationship between Alu retroelements, LTL, and lung cancer is unknown. Therefore, we investigated associations between Alu copy number, LTL, and lung cancer risk in the prospective Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial.
We conducted a nested case-control study of 410 confirmed incident lung cancer cases and 416 controls individually matched on age, sex, race/ethnicity, study center, and blood draw date. Quantitative PCR was used to measure Alu copy number and telomere length relative to albumin (Alb) copy number (Alu/Alb and T/S ratio, respectively) in pre-diagnostic leukocytes. Conditional logistic regression was used to estimate associations between quartiles (Q) of Alu/Alb ratio (reference=Q1) and lung cancer risk, adjusted for matching factors, smoking status and packyears, and LTL. Additionally, we dichotomized Alu/Alb ratio and LTL at their medians and created a cross-combination variable to assess combined effects.
We found a positive dose-response relationship between Alu/Alb ratio and lung cancer risk (odds ratio (OR), 95% confidence intervals (CI): Q2: 1.34 (0.73, 2.48); Q3:1.89 (0.94, 3.84); Q4: 2.66 (1.03, 5.63); p-trendordinal=0.02). The association was apparent for lung adenocarcinoma (LUAD) (Q2: 1.32 (0.46, 3.77); Q3: 2.88 (0.90, 9.25); Q4: 5.07 (1.29, 19.87); p-trendordinal=0.02). We have previously reported that longer measured LTL was also associated with an increased risk of LUAD (Q4: 2.82 (1.16-6.85); p-trend=0.011). The combined effect of both a higher Alu/Alb ratio and longer LTL was 6.07 (1.75, 21.04; p=4.5x10-3) for LUAD compared with lower/shorter levels of both.
Higher Alu copy number and longer LTL were associated with increased risk of lung cancer, especially LUAD. Our findings require replication. If confirmed, evaluation of Alu copy number and LTL in risk stratification and prediction analyses is warranted.
Citation Format: Jason Yat-Yang Wong, Richard Cawthon, Wei Hu, Somayina Ezennia, Shahinaz Gadalla, Charles Breeze, Batel Blechter, Neal Freedman, Wen-Yi Huang, H. Dean Hosgood, Wei Jie Seow, Bryan Bassig, Mohammad Rahman, Richard Hayes, Nathaniel Rothman, Qing Lan. Alu retroelement copy number, leukocyte telomere length, and lung cancer risk in the prospective Prostate, Lung, Colorectal and Ovarian Cancer (PLCO) Screening Trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2251.