In various aspects and embodiments the invention provides a method of treating or preventing a cancer in a mammalian subject in need thereof, the method comprising administering to the subject a therapeutically effective amount of at least one compound selected from the group consisting of a DNA repair inhibitor, a DNA strand break repair inhibitor, and a homologous recombination (HR) repair inhibitor, wherein cells in the cancer comprise a fumarate hydratase (FH) and/or succinate dehydrogenase (SDH) mutation.