FH is an enzyme of the TCA cycle that catalyzes the hydration of fumarate to malate.108 The inhibition of Heme Oxygenase 1 (HMOX1) results in a significant reduction in the growth of fumarate hydratase 1 deficient tumor cells but has little or no effect on normal cells.99 Thus, there is a synthetic lethal effect between HMOX1 and FH1 that targets mitochondrial function (Fig. 5). This evidence concerns the gene HMOX1 and neoplasm.