This study is testing a new medicine, JNJ-88549968, for people with specific blood disorders called *myeloproliferative neoplasms*, such as *essential thrombocythemia (ET)* and *myelofibrosis (MF)*. These are conditions where the bone marrow makes too many blood cells. The study aims to find the safest dose and the best schedule to give this medicine. It will first test increasing doses (Dose Escalation) and then see how well it works at the best dose (Cohort Expansion).
To join, you must be at least 18 years old and have a specific mutation in your blood cells. You cannot participate if you have certain other health conditions or allergies, or have had certain treatments like organ transplants. Participants will receive either JNJ-88549968 alone or with other treatments if they have MF.
Key Points:- Study involves two parts: finding the right dose and testing it.
- Participants must be positive for a CALR mutation.
- Some people will receive additional treatments for MF.