This study is being conducted to evaluate INCA033989 versus best available therapy in participants with essential thrombocythemia and a CALR mutation previously treated with cytoreductive therapy.
Confirmed diagnosis of high-risk ET.
Presence of mutCALR.
Prior treatment with at least 1 cytoreductive therapy.
Presence of any hematologic malignancy other than ET.
Major bleeding or thrombosis within the last 3 months prior to study enrollment.
Any prior allogenic or autologous stem-cell transplantation.
Unresolved toxicity ≥ Grade 2 from previous therapy except for stable chronic toxicities (Grade 2) not expected to resolve, such as stable Grade 2 peripheral neuropathy.