This will be a Phase 1, multicenter, open-label trial to evaluate the safety, tolerability, PK and efficacy of ZN-A-1041 as a monotherapy or in combination in participants with HER2-positive advanced solid tumors with or without brain metastases.

The study will consist of three phases: Phase 1a (dose escalation with ZN-A-1041 monotherapy), Phase 1b (dose escalation with ZN-A-1041 combination therapy) and Phase 1c (dose expansion with ZN-A-1041 combination therapy).

This study is composed of three parts designed to evaluate the safety and efficacy of ZN-A-1041 in participants with HER2-positive advanced solid tumors.

Phase 1a (Monotherapy Dose Escalation): In this first phase, participants will receive ZN-A-1041 alone. The study will begin with a low dose of ZN-A-1041, which will be gradually increased in new groups of participants to find the highest dose that can be given safely. This will establish the recommended dose for further study.

Phase 1b (Combination Dose Escalation): In the second phase, the study will evaluate the safety of giving ZN-A-1041 together with established standard-of-care therapies for HER2-positive breast cancer. Participants will be enrolled into one of three combination arms to receive ZN-A-1041 with either T-DM1, T-DXd, or a pertuzumab/trastuzumab-based regimen. This phase will identify the recommended dose for these combination therapies.

Phase 1c (Combination Dose Expansion): In the final phase, additional participants will be enrolled to receive ZN-A-1041 at the recommended combination doses identified in Phase 1b. This will allow for a more thorough evaluation of the safety and preliminary efficacy of these treatment regimens.

Throughout the study, participants will undergo screening, treatment, and follow-up periods to collect comprehensive data on the safety, tolerability, pharmacokinetics, and anti-tumor activity of ZN-A-1041, both as a single agent and in combination.

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• Life expectancy of at least 6 months, as determined by the investigator
• Histologically or cytologically confirmed with unresectable or metastatic HER2-positive advanced solid tumors
• Must be relapsed or refractory after prior treatment for metastatic disease that included a taxane and trastuzumab or must have received first-line induction therapy for advanced disease a pertuzumab plus trastuzumab-based regimen or a T-DXd-based regimen
• Participants with new, untreated, progressive, or stable brain metastases are eligible

Exclusion Criteria:

• Participation in any other clinical study involving an investigational drug or device within 4 weeks prior to the first dose of study treatment
• Any intracranial lesion (brain metastasis) that requires immediate local therapy, such as surgery or radiation, or systemic corticosteroids at the time of enrollment

For eligible studies, qualified researchers may request access to individual patient level clinical data. See Roche's commitment to transparency of clinical study information here: https://go.roche.com/data\_sharing