The study is divided into three periods: a screening period, study drug period, and follow-up period. If you choose to join the study, you will:

• Go through a screening period which lasts no more than 28 days
• Agree to send a blood sample for genetic testing
• Have blood and urine tests, EKGs, ECHO, and physical exams
• Have tumor evaluation by CT, MRI, or PET-CT

Study Drug Period: During this period of the study, you will get a random assignment (like a coin flip) to take either the study drug or a placebo (inactive substance with no drug in it).

• You will take the study drug or placebo once per day (2 pills)
• Neither you nor your study doctor will know if you are getting the study drug or placebo
• During study procedures, one "drug cycle" equals 28 days

OPTION TO CROSSOVER: If your condition gets worse, the study doctor will find out whether you have been taking placebo or ivosidenib. If you are taking the placebo, your study doctor will decide whether you are eligible to crossover to the study drug. If you are eligible and decide to pursue this option, you will then restart the same assessment schedule described in the study drug period. We will schedule you to come in for follow-up visits to see how you are doing after you stop taking the study regimen. We will continue to keep in touch with you for at least one year after you stop the study.