A First-in-Human Study of MEN2312 in Adults With Advanced Breast Cancer

Key Inclusion Criteria:

• Participant has advanced (locoregionally recurrent or metastatic) breast cancer notamenable to curative therapy.

• Participant must have received at least one prior line of endocrine therapy foradvanced/metastatic disease or participant who has radiological evidence of breastcancer recurrence or progression during or within 12 months from the end of orduring adjuvant treatment with endocrine therapy, as these participants areconsidered as first-line relapsed participants. Progression on previouscyclin-dependent kinase 4/6 inhibitor treatment in combination with fulvestrant oraromatase inhibitor is required. No other therapeutic options are consideredappropriate by the investigator.

• Up to 6 prior lines of systemic therapy (including up to 2 prior lines consisting ofchemotherapy, cytotoxic antibody drug conjugate, or a combination of both regimens)are allowed in the advanced/metastatic setting.

• Presence of genetic alterations in PIK3CA/AKT1/PTEN in participants' tumor tissue.

Key Exclusion Criteria:

• Active or newly diagnosed central nervous system metastases.

• Participants with advanced, symptomatic visceral spread, who are at risk oflife-threatening complications in the short term, including massive uncontrolledeffusions (peritoneal, pleural, pericardial), pulmonary lymphangitis, or liverinvolvement >50%.

Note: Other inclusion/exclusion criteria may apply.