Study to Assess Safety, Tolerability and Activity of DSB2455 in Participants With Advanced Malignancies

Inclusion Criteria: * The participant (or legally acceptable representative, if applicable) provides written informed consent for the study. * Aged ≥18 years of age on the day of signing the informed consent. * Has measurable disease per RECIST v1.1, or non-measurable disease as defined in the protocol. * ECOG performance status of 0 to 1. * Life expectancy \>12 weeks. * Adequate organ function as defined in the protocol. * Willing and able to comply with scheduled visits (including follow-up visits), and protocol procedures. * Willing and able to undergo imaging procedures as per protocol. * Willing to provide blood samples for correlative research purposes. * Able to swallow oral medication as an intact dosage form. * Prior intervention with an approved non-selective PARP inhibitor is permitted in Dose Escalation only. * Histologically confirmed diagnosis of locally advanced and/or metastatic breast cancer, prostate cancer, ovarian cancer, or pancreatic ductal adenocarcinoma with confirmed gene alterations as defined in the protocol. * Has received prior cancer treatment as outlined in the protocol, dependent on disease type. * Known asymptomatic or symptomatic brain metastasis, as confirmed by an MRI brain scan, from a primary tumour and meeting the eligibility for the disease types noted above (Dose Expansion only). Exclusion Criteria: * Myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML) or features suggestive of MDS/AML. * Has received a prior PARP1-selecti…