Study of INCA036978 in Participants With Myeloproliferative Neoplasms

Inclusion Criteria: * Life expectancy \> 6 months. * Willingness to undergo a pretreatment and limited on-study BM biopsies and aspirates (as appropriate to disease). * Participants with MF, PV and ET as defined in the protocol. Exclusion Criteria: * Presence of any hematological malignancy other than MF, PV, or ET. * Malignancy within the last 3 years prior to enrollment. * Acute or chronic HBV, Active HCV or known HIV or tuberculosis infection. * Clinically significant or uncontrolled cardiac disease. * Has undergone any prior allogeneic stem-cell transplantation or such transplantation is planned in the next 6 months. * Laboratory values outside the Protocol-defined ranges. * Prior history of major bleeding or thrombosis within the last 3 months prior to study enrollment. * Presence of chronic or current active infectious disease requiring systemic treatment. * Treatment with an MPN-directed therapy (approved or investigational) within the per protocol threshold before the administration of study drug. * Prior radiation therapy within 28 days before the first dose of study treatment. Other protocol-defined Inclusion/Exclusion Criteria may apply.