This is a Phase 1/1b, open-label, dose-escalation, and dose-expansion study to evaluate the safety, tolerability, pharmacokinetic (PK), pharmacodynamic (PD), and clinical activity of etrumadenant (AB928) in combination with pegylated liposomal doxorubicin (PLD) with or without IPI-549 in participants with advanced metastatic triple-negative breast cancer (TNBC) or ovarian cancer, and etrumadenant in combination with nanoparticle albumin-bound-paclitaxel (NP) in participants with advanced metastatic TNBC.

In the dose escalation phase, the following will be assessed:

• Arm A: escalating doses of etrumadenant in combination with PLD at standard doses will be assessed in participants with advanced metastatic triple-negative breast cancer or ovarian cancer. Eligible participants will receive oral administration of etrumadenant as well as intravenous (IV) infusion of PLD. The recommended dose (RDE) for expansion Arms 1 and 2 and escalation Arm C will be determined upon completion of this dose escalation arm.
• Arm B: escalating doses of etrumadenant in combination with the NP at standard doses will also be assessed in participants with advanced metastatic TNBC. Eligible participants will receive oral administration of etrumadenant as well as NP infusion. The RDE of etrumadenant will be determined upon completion of this dose escalation arm.
• Arm C: escalating doses of IPI-549 in combination with the RDE of etrumadenant (from Arm A) and PLD at standard doses will be assessed in participants with advanced metastatic TNBC or ovarian cancer. Eligible participants will receive oral administration of both etrumadenant and IPI-549 as well as IV infusion of PLD. The RDE of IPI-549 for expansion Arm 4 will be determined upon completion of this dose escalation arm.

In the dose expansion phase, the following will be assessed:

• Arms 1 and 2: Etrumadenant at the RDE in combination with PLD at standard doses may be assessed in participants with advanced metastatic TNBC or ovarian cancer.
• Arm 3: Etrumadenant at the RDE in combination with NP at standard doses may be assessed in participants with advanced metastatic TNBC.
• Arm 4: Etrumadenant and IPI-549 at the RDE in combination with PLD at standard doses may be assessed in participants with advanced metastatic TNBC.

Overall duration of treatment will depend on how well the treatment is tolerated. Treatment may continue until unacceptable toxicity or progressive disease or other reasons specified in the protocol.

Inclusion Criteria:

• Female participants, 18 years or older

• Measurable disease per radiographic evaluation

• Performance status 0 or 1

• Available archival tissue sample (within 2 years) or a fresh tumor biopsy may be required

• Adequate organ, cardiac, and bone marrow function

• Dose escalation

  • Participants with breast cancer:

    • Locally advanced or metastatic triple negative breast cancer (ER-negative, PgR-negative, and HER2-negative according to ASCO/CAP guidelines) with disease progression
    • No available alternative or curative therapy
    • Participants may have received any number of prior therapies for advanced/recurrent and progressive disease

  • Participants with ovarian cancer:

    • Locally advanced or metastatic ovarian cancer with disease progression
    • No available alternative or curative therapy
    • Participants may have received any number of prior therapies for advanced/recurrent and progressive disease

• Dose expansion

  • Participants with breast cancer:

    • Locally advanced or metastatic triple negative breast cancer (ER-negative, PgR-negative, and HER2-negative according to ASCO/CAP guidelines)
    • Disease progression after no more than 3 prior lines of therapy

  • Participants with ovarian cancer:

    • Locally advanced or metastatic ovarian cancer that is platinum-resistant
    • Disease progression after no more than 3 prior lines of therapy

Exclusion Criteria:

• Received a live, attenuated vaccine within 4 weeks prior to first study treatment
• Prior anticancer treatment including approved agents, systemic radiotherapy, or investigational therapy within 4 weeks prior first study treatment
• Cancer other than the disease under study within 2 years prior to study entry, except for some cancers with a low risk of spreading like non-melanoma skin cancers
• Inability to swallow oral medications
• Participant is breastfeeding, pregnant, or expects to become pregnant during the study
• Active autoimmune disease or documented history of autoimmune disease within 2 years prior to first study treatment
• History of peptic ulcer or stomach bleeding within 6 months prior to first study treatment
• Use of drugs contraindicated by the protocol within 4 weeks prior to and during study treatment
• Prior treatment with drugs that suppress the immune system within 2 weeks prior to first study treatment
• Presence of metastases in the brain or cancer spreading into the cerebrospinal fluid - CSF (leptomeningeal disease)
• HIV, Hepatitis B, and C test results negative prior to first study treatment
• Major surgery within 4 weeks prior to first study treatment
• Participants who have previously received maximum cumulative lifetime anthracycline dosage or baseline ejection fraction <50% (on heart echography)

Arcus will provide access to individual de-identified participant data and related study documents (e.g., protocol, Statistical Analysis Plan [SAP], Clinical Study Report [CSR]) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions.

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