Pharmacokinetics and Safety Study of Pelabresib in Patients With Advanced Malignancies and Hepatic Impairment

Key Inclusion Criteria: * Is at least 18 and not older than 75 years of age at the time of signing the informed consent. * Group 1 only: There is a matching participant in Group 2 and an enrollment slot is available for the Group 1 participant. * Has a confirmed documented diagnosis of an advanced malignancy for which no standard and/or curative treatment options are available. * Has the following acceptable laboratory assessments prior to the first dose of study treatment: 1. Platelet count ≥ 150 × 109 /L in the absence of thrombopoietic factors or transfusions within 2 weeks of the screening assessment 2. Absolute neutrophil count (ANC) ≥ 1 × 109 /L in the absence of granulocyte growth factors 3. Adequate renal function (creatinine clearance of ≥30 mL/min, calculated using Cockcroft-Gault formula) 4. Peripheral blood blast count \< 5%. Assessment of blasts in bone marrow is not mandatory at screening, however, blasts must be \<5% if the assessment is performed. * Has a life expectancy ≥3 months. * Has fully recovered from major surgery and from the acute toxic effects of prior chemotherapy and radiotherapy . * Hepatic function: 1. Is in Group 1 and is classified as having normal hepatic function based on NCI-ODWG criteria (i.e., total bilirubin ≤ upper limit of normal (ULN) and aspartate aminotransferase (AST) ≤ ULN); or 2. Is in Group 2 and has stable moderate or severe HI as defined by NCI ODWG criteria: * moderate HI: total bilirubin \>1.5 × to 3 × ULN, and any AST value * severe HI: total bilirubin \> 3 × ULN, and any AST value Key Exclusion Criteria: * Has a history of hypersensitivity to the study treatment or its excipients or to drugs of similar chemical class. * Has any other medical condition which, in the investigator's opinion, makes the participant unsuitable for the study. * Is a female participant who is pregnant (confirmed by a pregnancy test at screening) or is breastfeeding. * Is a woman of childbearing potential (WOCBP) who does not agree to follow the contraceptive guidance during the treatment period and for at least 184 days after the last dose of study treatment, and who does not agree to refrain from donating eggs during this period. * Has esophageal variceal bleeding within the past 2 months prior to the first dose of pelabresib. * Has an active clinically significant infection. * Has impaired cardiac function or clinically significant cardiac diseases * Has a GI tumor, impaired GI function, GI disease, or significant resection of stomach or other portion of the GI tract that could alter the absorption of pelabresib, including any unresolved nausea, vomiting, or diarrhea. Other protocol-defined inclusion/exclusion criteria may apply.