In this study, people will take a special medicine called PLX-61639 one time each day. Before starting, there will be a time called the screening period that can last up to 28 days. During this time, doctors will check to see if you can join the study. After that, you will take the medicine in 28-day cycles. You will go to the clinic often for check-ups. These visits will include blood tests, heart tests, and scans. Some visits might take the whole day. You will also write in a diary to keep track of when you take the medicine. The amount of medicine you get may be different depending on when you join the study. You can stay in the study as long as the doctor thinks the medicine is helping you.