PROJECT SUMMARY/ABSTRACT The Training in Oncology Population Sciences (TOPS) T32 program will train postdoctoral fellows to conduct research at the T3 and T4 interface to translate knowledge from the lab into practice and population health to reduce the burden of cancer. The need for translational research at the T3 and T4 interface stems from persistent disparities in cancer outcomes and implementation gaps between what is possible in the context of clinical trials and what happens in routine practice. The TOPS program will train 3 postdoctoral fellows each year in collaboration with 36 faculty from across the 7 institutions of the Dana-Farber/Harvard Cancer Center. Training will provide fellows with the skills necessary to address the challenges and opportunities brought about by the tremendous growth in the complexity of cancer care, precision medicine, electronic health records, mobile health, machine learning and data sharing. The TOPS program has 3 specific strategies to achieve this overarching objective: 1) training in core methods and skills necessary for investigation through coursework and participation in regular seminars, workshops and reading; 2) intensive focus on a research project with close supervision from one or more mentors; and, 3) training in professional skills that are prerequisite for investigation including project development, grant writing, presentation, building and working with diverse teams, running a dry-laboratory and the responsible conduct of research. The TOPS T32 proposal is a renewal of the successful R25CA092203 Program in Cancer Outcomes Research Training (PCORT), which trained 41 pre- and post-doctoral fellows between 2002 and 2017. TOPS will be co- led by Dr. Nancy Keating, a primary care physician, and Dr. Deborah Schrag, a medical oncologist, both accomplished cancer-focused population scientists who served on the PCORT Steering Committee and trained numerous fellows who have become independent researchers. TOPS intends to train postdoctoral students with degrees in the fields of medicine, nursing, behavioral science, pharmacy, economics, clinical epidemiology, health policy, informatics, and engineering for careers dedicated to cancer-focused population science. The core of the program is a group of 36 faculty mentors and 13 emerging mentors with expertise in quality measurement, design of patient, clinician, community and health system-level interventions, conduct of pragmatic trials, comparative effectiveness research, analysis of survey, administrative and electronic health record data, and expertise in organizational and behavioral strategies that optimize implementation. At the end of the two-year training, TOPS program participants will be well-equipped with the skills necessary to launch independent research careers in cancer-focused population science and have access to the core resources of the DF/HCC and the Harvard Catalyst program for translational research training. The TOPS co-directors and are supported by an 8-member Steering Committee that includes leaders from each of the 7 institutional members of the DF/HCC and 6 accomplished investigators in population science who will serve as Advisors.