Abstract Background: The process of tumor evolution has often been described as a single initiated cell propagating a tumor with subclones of that cell acquiring distinct molecular changes and competing for dominance within the tumor. However, colon tumors are now known to often be derived from multiple initiated progenitor cells. Distinct initiated clones might cooperate or alternatively compete during tumorigenesis, progression, and therapy. Methods: Mice carrying the Min allele of Apc and expressing an oncogenic form of PI3K in a subset of colonic epithelial cells develop multiple adenomas and adenocarcinomas in the colon. We utilized cell lineage tracing to follow the progeny of individual progenitor cells through tumor establishment, progression, and treatment with GDC 0941, a PI3K inhibitor. Results: Nearly half (44%; 30/68) of the tumors were derived from at least two progenitor clones, one of which expressed the oncogenic form of PI3K and one of which did not. The presence of both types of clones correlated to an increased frequency of either clone becoming invasive (p = 0.0002). Additionally, the presence of both clones appeared to protect susceptible clones from targeted therapy. Conclusions: Taken together, these data indicate that genetically distinct tumor progenitors can establish a single lesion, and moreover cooperation amongst diverse clonal populations provides a fitness advantage during tumor progression and therapy. Citation Format: Alyssa A. Leystra, Amanda M. Wisinger, Christopher D. Zahm, Kristina A. Matkowskyj, Chelsie K. Sievers, Alex Schwartz, Dawn M. Albrecht, Linda Clipson, Dustin A. Deming, Michael A. Newton, Richard B. Halberg. Discrete clones cooperate to promote tumor progression through a non-cell-autonomous mechanism in intestinal cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4143. doi:10.1158/1538-7445.AM2015-4143