Ivosidenib for Patients With Clonal Cytopenia of Undetermined Significance and Mutations in IDH1

Inclusion Criteria: * Unexplained cytopenia for at least 6 months. Cytopenia is defined as the presence of ≥1 blood count indexes below the following thresholds: * Hgb \<10 g/dL * ANC \<1.8 × 10\^9/L * Platelets \<100 × 10\^9/L * IDH1 gene mutation (R132) confirmed by droplet digital PCR (ddPCR) testing, at a frequency \> 2%. This will be performed locally and confirmed at Washington University. * At least 18 years of age. * ECOG performance status 0-2 * Adequate organ function as defined below: * AST(SGOT)/ALT(SGPT) ≤ 3.0 x IULN * Serum total bilirubin \< 1.5 x IULN (an upper limit of bilirubin 5mg/dL is acceptable if it can be attributed to Gilbert's syndrome or erythropoiesis) * Serum creatinine \< 2 x IULN or creatinine clearance \> 50 mL/min by Cockcroft-Gault glomerular filtration rate estimation * The effects of ivosidenib on the developing human fetus are unknown. For this reason, women of childbearing potential and men must agree to use adequate contraception (defined in Section 5.5) prior to study entry, for the duration of study participation, and for 90 days after the last dose of ivosidenib. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of the study, and for 90 days after the last dose of ivosidenib. * Ability to understand and w…