A Clinical Study of Boserolimab (MK-5890) With Pembrolizumab and Chemotherapy in People With Early Triple-Negative Breast Cancer (MK-5890-003)

Inclusion Criteria:

The main inclusion criteria include but are not limited to the following:

• Has previously untreated high-risk, early-stage, non-metastatic (M0) breast cancer (BC), defined as tumor stage T1c, nodal stage N1-2, or tumor stage T2-4, nodal stageN0-2

• Has provided a core needle biopsy for tissue diagnosis of the current breast cancerless than 29 days prior to the date of informed consent

• Has centrally confirmed diagnosis of BC that is triple-negative based on theAmerican Society of Clinical Oncology/College of American Pathologists guidelines

• Has Eastern Cooperative Oncology Group performance status of 0 or 1 performed within 28 days before treatment randomization

• Has left ventricle ejection fraction of ≥50% as assessed by echocardiogram ormultigated acquisition scan performed at screening

• Has a history of exposure to anthracycline; participants can be eligible aftercompletion of a Sponsor consultation form, if cumulative lifetime doses are asfollows: Doxorubicin <100 mg/m2, Epirubicin <180 mg/m2, Mitoxantrone <40 mg/m2,Idarubicin <22.5 mg/m2. Note: If another anthracycline or more than oneanthracycline has been used, the cumulative dose must not exceed the equivalent of 100 mg/m2 of doxorubicin

Exclusion Criteria:

The main exclusion criteria include but are not limited to the following:

• Has documented Grade ≥2 peripheral neuropathy

• Has uncontrolled or significant cardiovascular disease

• Has received prior therapy with an anti-programmed cell death protein 1 (anti-PD-1),anti-programmed cell death-ligand 1 (anti-PD-L1), or anti-PD-L2 agent, or with anagent directed to another stimulatory or coinhibitory T-cell receptor (e.g.,cytotoxic T-lymphocyte-associated protein-4 [CTLA-4], OX-40 [cluster ofdifferentiation (CD) 134], or CD137)

• Has received any prior treatment, including radiation, systemic therapy, and/ordefinitive surgery for currently diagnosed breast cancer

• Has received prior systemic anticancer therapy

• Has undergone excisional biopsy of the primary tumor and/or axillary lymph nodedissection prior to study treatment

• Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapyor any other form of immunosuppressive therapy within 7 days prior to the first doseof study intervention

• Has a known additional malignancy that is progressing or has required activetreatment within the past 5 years

• Has active autoimmune disease that has required systemic treatment in the past 2years with need for disease modifying agents such as corticosteroids orimmunosuppressive drugs

• Has history of (noninfectious) pneumonitis/interstitial lung disease that requiredsteroids or has current pneumonitis/interstitial lung disease

• Has an active infection requiring systemic therapy

• HIV-infected participants with a history of Kaposi's sarcoma and/or MulticentricCastleman's Disease

• Has severe hypersensitivity (Grade ≥3) to pembrolizumab, any investigational agentor study intervention, any of its excipients, and/or to another biologic therapy

• Has a history of allogeneic tissue/solid organ transplant