The orally active fumarate salt of the benzimidazole derivative liarozole with potential antineoplastic activity. As a retinoic acid metabolism blocking agent (RAMBA), liarozole inhibits cytochrome P450-dependent all-trans-retinoic acid (ATRA)-4-hydroxylase, resulting in an increase in endogenous ATRA production, inhibition of cell proliferation, and induction of cell differentiation. This agent also inhibits aromatase, the enzyme that catalyzes the final, rate-limiting step in estrogen biosynthesis.