PROJECT SUMMARY. Cancer survivors have unique healthcare needs including risk for serious late effects, ongoing surveillance, lifestyle modifications to reduce second cancer risk, and psychosocial support. Nearly 70% are considered “complex cancer survivors” because they have at least one comorbid chronic condition in addition to cancer. Comorbidities pose significant challenges to the delivery of quality cancer care because they adversely affect and are affected by cancer treatment. Medically underserved patients have the highest burden of multiple chronic conditions and are at increased risk for poor outcomes during and after cancer treatment. As medically underserved complex cancer patients may lack healthcare knowledge and access to supportive care, their health outcomes and care transitions might be improved by enhancing communication and collaboration between their oncologists and primary care providers (PCPs). This study tests and evaluates a novel shared care model for complex cancer survivors called OPTIMISE (Oncology-Primary Care Partnership to Improve Comprehensive Survivorship Care) in the largest safety-net healthcare system in Houston, TX. Three-hundred newly diagnosed breast, GI, and hematological cancer patients who are being treated with curative intent and who have comorbidities requiring ongoing management during cancer treatment will complete baseline surveys and be randomized to either OPTIMISE or Usual Medical Care (UMC). Patients receiving UMC will receive their cancer treatment, as directed by their oncologist, a survivorship care plan (SCP) at the end of active treatment, and surveillance visits with their oncologist based on national guidelines. Patients in OPTIMISE will 1) have an oncology nurse navigator assigned to their care team at diagnosis to facilitate oncologist-PCP communication and continuity of care; 2) receive coordinated care between their oncologist and PCP throughout cancer treatment and surveillance facilitated by a structu