Abstract PL03-01: New insights into carcinogenesis from normal esophagus

Abstract

Abstract All normal tissues studied to date carry somatic mutant clones, the burden of which increases with age. This talk considers how insights into the biology of mutants in normal tissues can inform our understanding of the earliest stages of carcinogenesis. The esophagus becomes a patchwork of mutant clones. As they expand, these clones compete for the limited space available, resulting in selection of the fittest mutant genes. The ability to out compete other mutants in normal tissue does not correlate with carcinogenic potential. For example, NOTCH1 mutant clones colonize most of the esophagus by middle age but NOTCH1 mutations are comparatively rare in squamous cancers. In mouse models Notch pathway mutant clones eliminate microscopic intraepithelial neoplasms and loss of Notch1 markedly slows esophageal tumor growth. In contrast, mutant TP53 is less effective than NOTCH1 at driving clonal expansion but is found in almost all human squamous esophageal cancers and contributes to carcinogenesis in mice. The normal tissue mutational landscape of the esophagus is shaped by environmental factors. For example, body metabolism alters the behavior of mutant PIK3CA which drives clonal expansions in the esophagus of overweight humans and mice. The mutation causes cells to switch their metabolism to aerobic glycolysis, giving the mutants a proliferative advantage. One way to reduce the competitive advantage of mutants is to increase the fitness of the neighboring cells. Treating cells or mice with metformin, a drug used to treat type 2 diabetes, induces aerobic glycolysis throughout the tissue. This eliminates the growth advantage of Pik3ca mutant clones, showing it may be possible to halt the expansion of oncogenic mutant populations. Beyond the esophagus, these findings suggest the need to consider the relative prevalence of mutations in normal tissue and the corresponding cancer(s) before deciding if a mutant gene is a cancer driver or not. Variation in cancer risk between different human populations may depend on the proportion of pro- and anti-oncogenic mutants in normal tissue. Understanding how certain mutations can impede cancer development and how environmental factors alter selection of oncogenic mutants in normal tissue may guide new approaches to cancer prevention. Citation Format: Phil H. Jones. New insights into carcinogenesis from normal esophagus. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr PL03-01.