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.

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

• Participant must have received at least 1 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 adjuvanttreatment with endocrine therapy, as these participants are considered as first-linerelapsed participants.

• Progression on previous cyclin-dependent kinase 4 and 6 inhibitor treatment incombination with fulvestrant or aromatase inhibitor is required.

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%.

• Participants with any toxicities related to prior radiation therapy that have notresolved to baseline or to National Cancer Institute Common Terminology Criteria forAdverse Events v5.0 Grade ≤1, except alopecia and peripheral sensory neuropathy (Grade ≤2).

Note: Other inclusion/exclusion criteria may apply.