This is a sources-sought notice for a contract to maintain the Cleanup Workers Clinical Cohort in Ukraine, which involves updating demographic, clinical, and epidemiologic data for approximately 10,965 Chernobyl cleanup workers through mail surveys and passive follow-up via cancer registries. The contractor will be required to manage concurrent in-country studies, including updating vital status for at least 2,000 subjects annually and conducting record linkages to the National Cancer Registry of Ukraine and the State Chernobyl Registry. The anticipated period of performance is from July 1, 2027, through June 30, 2032, with a 12-month base period and four 12-month option periods. The location for performance of services is Ukraine, with work conducted at the National Research Center for Radiation Medicine, Hematology and Oncology in Kiev. No budget amount is specified in this notice.