This study is looking at a medicine called pelabresib, combined with another medicine, ruxolitinib, to see if they work better together than just ruxolitinib alone for people with a blood problem called myelofibrosis (MF). Myelofibrosis is a bone marrow disorder that affects blood cell production.

The study has different parts: first, a screening period to check if you can join, then a treatment period where you get the medicines, and finally, a follow-up period to see how you're doing after treatment. The treatment is given in cycles of 21 days, with pelabresib for 14 days and ruxolitinib continuously. There are regular check-ups to monitor your health.

• The treatment lasts until you stop responding, have side effects, or choose to leave.
• You cannot participate if you’ve had certain other treatments or surgeries recently.
• Regular follow-ups are needed to ensure your safety and the study's effectiveness.