Individuals and families with known or suspected syndromes that include breast, ovarian or genetically-related cancers are enrolled in this family study, which is a syndrome-specific sub-set of the long-standing DCEG Human Genetics Program umbrella family studies protocol (78-C-0039). Cancer outcomes are documented through review of medical, vital, and pathology records. Selected individuals and family members are asked to complete questionnaires to assess etiologic risk factors and to undergo clinical evaluations specifically tailored to the relevant familial syndrome. Study participants are monitored prospectively for the development of outcomes of interest, typically by means of periodic mail or telephone contact. In selected instances, subjects may return to the Clinical Center periodically for study-specific follow-up examinations. Study participants are asked to donate biologic specimens to be used in the laboratory search for cancer etiology and mechanisms of carcinogenesis. DNA and serial serum samples will be collected. Tumor tissue will be obtained whenever feasible.