The present invention provides diagnostic and prognostic methods for predicting the effectiveness of treatment of a cancer patient with a DHODH inhibitor or an antimetabolite. Methods are provided for predicting the sensitivity of tumor cell growth to inhibition by a DHODH inhibitor or an antimetabolite, comprising assessing whether the tumor cell comprises a mutant IDH gene or protein whereby cells that comprise a mutant IDH gene or protein are sensitive to inhibition by DHODH inhibitors and antimetabolites.