A Study Evaluating Safety and Tolerability, and Pharmacokinetics of Navitoclax Monotherapy and in Combination With Ruxolitinib in Participants With Myeloproliferative Neoplasm

Inclusion Criteria

• •Parts 1 and 2:
• •Navitoclax Monotherapy (Part 1 Only - Japanese Participants):
• •* Documented diagnosis of myelofibrosis (MF), polycythemia vera (PV) or essential thrombocythemia (ET) as defined by the World Health Organization (WHO) classification.
• •* MF participants must have received and failed or are intolerant to ruxolitinib therapy.
• •* ET or PV participants must be requiring cytoreduction who have failed or are intolerant to at least one prior therapy, or who refuse standard therapy.
• •Navitoclax + ruxolitinib Combination Therapy (Part 2 Only - Japanese and Taiwanese Participants):
• •* Has documented diagnosis of primary MF, post-polycythemia vera MF (PPV-MF), or post-essential thrombocythemia (PET-MF) as defined by the World Health Organization (WHO) classification.
• •* Is ineligible or unwilling to undergo stem cell transplantation at time of study entry.
• •* Has splenomegaly as defined by a spleen palpable \>= 5 cm below costal margin or spleen volume \>= 450 cm\^3 as assessed by magnetic resonance imaging (MRI) or computed topography (CT) scan.
• •* Must have received ruxolitinib therapy for at least 12 weeks and be currently on a stable dose of ruxolitinib (as described in the protocol).
• •Must have adequate bone marrow, kidney, liver and hematology blood values as detailed in the study protocol.
• •Part 1 only: Cytoreduction for participants with ET and PV therapy within 14 days prior to the first dose of navitoclax will be allowed pending additional discussion with study doctor. Ruxolitinib for MF participants will not be allowed within 7 days prior to the first dose of study drug and during navitoclax administration.
• •Eastern Cooperative Oncology Group (ECOG) performance status \<= 1.
• •Part 3, and Part 4 (Participants in US and Europe):
• •Part 3 Only: At screening or baseline (pre-dose on Day 1), participant has QT interval corrected for heart rate (QTc) interval by Fridericia's correction (QTcF) \<= 450 msec.
• •Participants with a documented diagnosis of primary or secondary MF, ET, PV or chronic myelomonocytic leukemia (CMML) as defined by the WHO classification.
• •Participants must be requiring treatment and have failed or are intolerant to at least one prior therapy or who refuse standard therapy.
• •ECOG performance status \<= 2.
• •Must have adequate bone marrow, kidney, liver and hematology blood values as detailed in the study protocol.
• •Part 5 (Participants in US and Europe):
• •Has a documented diagnosis of primary MF as defined by the WHO classification, post-polycythemia vera (PV) MF, or post-essential thrombocythemia (ET) MF.
• •Classified as intermediate-2 or high-risk MF, as defined by the Dynamic International Prognostic Scoring System (DIPSS).
• •Requiring treatment for MF and must either have no prior treatment with a JAK2 inhibitor or have received treatment with ruxolitinib as noted in the protocol.
• •Have an ECOG performance status \<=2.
• •Have adequate bone marrow, kidney, liver and hematology blood values as detailed in the protocol.