PROJECT SUMMARY/ABSTRACT The Cancer Epidemiology and Population Science (CEPS) research program focuses primarily on cancer in Iowa, the Holden Comprehensive Cancer Center (HCCC) catchment area, while recognizing that its impact extends well beyond the state. The primary goal of the CEPS is to conduct population-based research that improves our understanding of cancer etiology, morbidity, and mortality in order to explore interventions for reducing cancer incidence and mortality and improving quality of life for cancer survivors. This is accomplished through three related research aims centered on 1) cancer etiology, 2) primary and secondary cancer prevention and 3) cancer health care services and outcomes. Recent influential CEPS publications have addressed lymphoma, chronic lymphocytic leukemia, contralateral breast cancer, pancreatic and breast cancer survival, stress, and end-of-life issues, as well as United States Preventive Services Task Force recommendations for cancer prevention and screening. CEPS membership includes 28 full and nine associate members spanning 17 departments across five colleges. Annual total direct funding for peer-reviewed research in the last budget year was $4.3 million with $1.5 million from the NCI. CEPS members are highly productive, having authored or co-authored 372 cancer-related peer-reviewed publications since 2016, and highly collaborative, with 24% (n=91) intraprogrammatic, 18% (n=70) interprogrammatic, and 63% (n=235) interinstitutional publications. Fifty-two of these publications appeared in high impact journals (Impact Factor >10). Successful intra/interprogrammatic and multi-institutional collaborations are generating important cancer- related advances in knowledge about pesticide and polychlorinated biphenyl exposures; lymphoma, sarcoma, and cancers of the breast, ovary, and colorectum; HPV-related cancer and vaccination; multimorbidity science; cancer screening; and tobacco cessation.