• Ability to comprehend and willingness to sign a written informed consent form (ICF) for the study.

• Age above 18 years inclusive at the time of signing the ICF.

• Participants who fulfill the diagnostic criteria of myelofibrosis including primary myelofibrosis and myelofibrosis arising from polycythemia vera and essential thrombocythemia

• Life expectancy is greater than 6 months.

• Subject has been receiving ruxolitinib therapy, is unlikely to benefit from further ruxolitinib monotherapy in the opinion of the investigator; AND meeting the following criteria: receiving ruxolitinib \>3 months prior to enrollment; AND stable dose for 8 weeks before starting therapy with CK0804

• Subject with evidence of evaluable residual burden of disease following ruxolitinib monotherapy treatment, consisting of:

‣ presence of grade ≥2 anemia or thrombocytopenia or neutropenia, OR

⁃ presence of disease-related symptoms, as determined by a Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score (MPN SAF TSS) score of ≥10 points, OR

⁃ documented splenomegaly of at least 5 cm below the costal margin as measured by physical examination or splenomegaly as documented by ultrasound or MRI.

• Willingness to avoid pregnancy or fathering children based on the criteria below

‣ Men must agree to take appropriate precautions to avoid fathering children (with at least 99% certainty) from screening through 90 days after the last study treatment dose and must refrain from donating sperm during this period. Permitted methods that are at least 99% effective in preventing should be communicated to the participants and their understanding confirmed.

⁃ Women of childbearing potential must have a negative serum pregnancy test at screening before the first dose (within 3 days of the first study treatment dose) and must agree to take appropriate precautions to avoid pregnancy (with at least 99% certainty) from screening through the safety follow-up visit and must not donate oocytes during this period. Permitted methods that are at least 99% effective in preventing pregnancy should be communicated to the participants and their understanding confirmed,

⁃ Women of nonchildbearing potential (ie, surgically sterile with a hysterectomy and/or bilateral oophorectomy OR ≥ 12 months of amenorrhea and at least 50 years of age) are eligible.

• ECOG performance status of 0 to 2