This trial investigates a new drug, EIS-12656, in participants with specified advanced solid tumors carrying pre-specified mutations. The trial consists of a dose escalation part (Phase 1) and a dose expansion part (Phase 2).

The trial is a Phase 1/2, open label, uncontrolled trial to investigate the safety and preliminary efficacy of EIS-12656 alone or in combination with a PARPi or T-DXd in patients with specified advanced or metastatic solid tumors with homologous recombination deficient (HRD) mutations.

In the Phase 1 dose escalation phase participants will receive ascending doses of EIS-12656 to evaluate the safety and tolerability and to determine an effective and safe dose for the Phase 2 part.

In the Phase 2 dose expansion phase participants will either receive EIS-12656 monotherapy at the recommended Phase 2 dose (RP2D) (Module 1) or EIS-12656 in combination with a PARPi or T-DXd (Modules 2 and 3). The objective is to evaluate the safety and tolerability and anti-tumor activity of EIS-12656 alone or in combination.

Inclusion Criteria:

• Recurrent locally advanced or metastatic solid tumors
• Homologous recombination deficient mutations
• Progressed on at least on prior line of treatment or intolerant to additional effective standard therapy
• Measurable disease (RECIST 1.1 Criteria)
• Adequate organ and bone marrow function
• ECOG Performance Status 0 or 1
• Life expectancy > 3 months

Exclusion Criteria:

• History or evidence of any clinically relevant gastrointestinal disease
• Radiation therapy within ≤2 weeks
• Significant cardiovascular disease
• Uncontrolled, active, symptomatic brain metastases