NSAIDS and Somatic Mutations in Barrett's Esophagus

Background: Use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) has been shown to protect against tetraploidy, aneuploidy, and chromosomal alterations in the metaplastic condition Barrett's esophagus (BE) and to lower the incidence and mortality of esophageal adenocarcinoma (EA). The esophagus is exposed to both intrinsic and extrinsic mutagens resulting from gastric reflux, chronic inflammation and exposure to environmental carcinogens such as those found in cigarettes. Here we test the hypothesis that NSAID use inhibits accumulation of point mutations/indels during somatic genomic evolution in BE. Methods: Whole exome sequences were generated from 82 purified epithelial biopsies and paired blood samples from a cross-sectional study of 41 NSAID users and 41 nonusers matched by sex, age, smoking, and continuous time using or not using NSAIDs. Results: NSAID use reduced overall frequency of point mutations across the spectrum of mutation types, lowered the frequency of mutations even when adjusted for both TP53 mutation and smoking status, and decreased the prevalence of clones with high variant allele frequency. Never smokers who consistently used NSAIDs had fewer point mutations in signature 17, which is commonly found in EA. NSAID users had on average a 50% reduction in functional gene mutations in nine cancer-associated pathways and also had less diversity in pathway mutational burden compared to nonusers. Conclusions: These results indicate NSAID use functions to limit overall mutations on which selection can act and supports a model in which specific mutant cell populations survive or expand better in the absence of NSAIDs. Galipeau PC, et al. Genome Med. 2018 Feb 27;10(1):17. PMID: 29486792.]]> Participants were drawn from The Seattle Barrett's Esophagus Study. 408 participants met the initial study inclusion criteria of having at least one endoscopy with endoscopic and histologic diagnosis of BE without EA, and who also provided detailed medical history with specific prescription and over-the counter medications including aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs). All biopsies in the study were collected between 13 February 1995 and 25 October 2011. Further exclusion criteria were only one endoscopy before EA diagnosis (N=4), external event including endoscopic mucosal resection and/or ablation during follow-up (N=30), inconsistent NSAID use across timepoints (N=221), focal or minimal Barrett's epithelium (N=24). Of the remaining 129 eligible participants of 72 consistent NSAID users and 57 consistent NSAID nonusers, a cross-sectional study was designed with each NSAID user randomly selected to a matched NSAID nonuser based on sex, age at baseline (within 10 years) and smoking status (never/ever across all endoscopies). 41 NSAID user:nonuser pairs met this matching criteria.]]> The Seattle Barrett's Esophagus Study (SBES), which was founded in 1983 as a prospective observational cohort study of patients with Barrett's esophagus (BE), and now comprises more than 900 patients and includes a biorepository of biospecimens and associated clinical and epidemiologic data. BE is the only known precursor to esophageal adenocarcinoma (EA), which has an estimated annual incidence of 0.5% to 1.0%, yet BE is primarily an indolent disease that will not progress to cancer during the lifetime of most patients. Yet the incidence of esophageal adenocarcinoma is known to be increasing at an alarming rate in many western countries, rising nearly 600% in the US over the three decades from 1972 - 2002. The overarching goals of the SBES are to (1) reduce morbidity and mortality of EA by early detection, prevention, or both and (2) elucidate mechanisms of human neoplastic progression in vivo that may be shared by other neoplasms whose early stages are less amenable to investigation. The study has over 30 years of experience in early translational research studies as defined by the NCI Translational Research Working Group (http://www.cancer.gov/trwg/TRWG-definition-and-TR-continuum). BE can be modulated by host and environmental risk and protective factors as well as generation of variants, natural selection and neoplastic evolution of clones within the Barrett's segment. In the 1980's the study developed the endoscopic biopsy protocols that are the current standard of care for cancer risk stratification in BE. During the late 1980s and early 1990s, the study established the scientific base for studying somatic genomic evolution longitudinally. In the 2000's, the study used techniques derived from early studies in yeast to determine the order in which genetic abnormalities developed over space and time ("clonal ordering") during progression from BE to EA. The study showed that neoplastic evolution was branched with non-linear bifurcations that occurred in no obligate order (Barrett et al., Nat Gen 1999, PMID: 10319873; Galipeau et al., JNCI 1999, PMID: 10601379). The intersection between aspirin and somatic genomic evolution is a complex biological system in which NSAID use introduces selective pressures on the evolving somatic genome that decrease progression to cancer in some patients but not others. In the inflammatory environment of Barrett's esophagus, there is an interaction between gene mutations and NSAIDs that modulate pathways leading to genomic instability and progression to cancer. In a previous study (Vaughan et al., Lancet Oncol 2005, PMID: 16321762), we showed that aspirin and other NSAIDs prevent cancer by reducing progression from early stages of BE to massive chromosomal instability manifested by tetraploidy and/or aneuploidy. This prospective study of 350 Seattle Barrett's Esophagus Study patients, followed for a median of 5.4 years found that the 5-year cumulative incidence of EA was 14.3% (95% CI 9.3-21.6) for never users compared to 6.6% (3.1-13.6) for current users (Hazard Ratio [HR] 0.20; 95% CI=0.10-0.41 compared to never users). This study also showed a decreased risk for progression to aneuploidy (HR=0.25; 95% CI 0.12-0.54 compared to never users) and tetraploidy (HR=0.44; 95% CI 0.22-0.87 compared to never users) in individuals with BE who were taking NSAIDs. A study by Galipeau et al., PLoS Med 2007, PMID: 17326708, showed that NSAIDs also act on subset of high risk BE to prevent progression to EA even when high-risk somatic chromosomal alterations such as 9p LOH, 17p (p53) LOH, tetraploidy and/or aneuploidy have already developed. In this study, aspirin or other NSAID use resulted in a strong and significant reduction of risk of progressing to EA (p<0.001). Interestingly, high risk individuals who were NSAID users and who had either two or all three chromosome instability markers at baseline showed the greatest reduction in risk of progressing to EA, with NSAID non-users having a 78% ten-year cumulative incidence of EA compared to only 28% for NSAID-users. A prospective observational cross-over study by Kostadinov et al., PLoS Genetics 2013, PMID: 23785299, evaluated 161 biopsies from 13 individuals with BE who changed their NSAID use once (user to non-user or vice versa) over an average of 11.6 years of follow-up (range 6.4-19 years) using 1M SNP arrays at 5-8 time points. Across all individuals, there was a significant increase in the acquisition of new SCAs while off NSAIDs as compared to when they were on NSAIDs (60 ± 166 vs. 28 ± 48 per biopsy, p=0.013). There was also a significant increase in the number of pre-existing SCAs (detected at, or after, baseline) that were no longer detected while on NSAIDs as compared to while off NSAIDs (92 ± 143 vs. 19 ± 21 per biopsy, p<0.01). These studies showed that aspirin and other NSAIDs decrease chromosomal instability, the most common type of genomic instability, at early and late stages of progression from BE to EA.]]>