A Study to Investigate the Safety, Tolerability, Pharmacokinetics (PK), and Preliminary Anticancer Activity of GSK4524101 Alone or With Niraparib in Participants With Solid Tumors

Inclusion Criteria

• More than or equal to (≥)18 years of age
• Eastern cooperative oncology group (ECOG) class 0-2
• Life expectancy of a minimum of 3 month
• Participant has histologically diagnosed advanced or metastatic solid tumor and has exhausted all standard of care treatment options (Part 1).
• Participant has metastatic, gBRCAmut, HER2-negative or HER2-low breast cancer who has completed at most 3 or more prior lines of therapy (Part 2).

Exclusion Criteria

• Participant has not recovered (i.e., to Grade less than or equal to [≤1] or to baseline) from prior chemotherapy-induced AEs.
• Participant is currently participating in a treatment study or has participated in a study of any investigational agent within 4 weeks of the first dose of treatment.
• Participant has symptomatic uncontrolled brain or leptomeningeal metastases.
• Participant has a known additional malignancy that progressed or required active treatment within the last 2 years
• Participant has a known history of Myelodysplastic syndrome (MDS) or Acute myeloid leukemia (AML).
• Participant has uncontrolled hypertension with sustained systolic blood pressure (BP) >140 millimetres of mercury (mmHg) or diastolic BP >90 mmHg.