Study Comparing Tobemstomig and Nab-Paclitaxel with Pembrolizumab and Nab-Paclitaxel for Untreated PD-L1-Positive Advanced Triple-Negative Breast Cancer

Inclusion Criteria

• Have advanced or metastatic triple-negative breast cancer that cannot be removed by surgery and has been confirmed by lab tests.
• Cancer must not show overexpression of HER2, estrogen, or progesterone receptors.
• Have HER2-low status.
• Have measurable cancer according to standard criteria.
• If the cancer has spread (Stage IV), it must be measurable outside the bones.
• Have not received any prior treatment for advanced or metastatic triple-negative breast cancer.
• Tumor must show PD-L1 expression confirmed by central testing.
• Be in good overall health with an ECOG performance status of 0 or 1, meaning fully active or restricted in physically strenuous activity but ambulatory.
• Have adequate blood and organ function.
• Test negative for HIV, unless stable on treatment with a CD4 count of 200/uL or more and undetectable viral load.
• Test negative for hepatitis B surface antigen and have either a positive hepatitis B surface antibody or a negative hepatitis B core antibody with low HBV DNA levels.
• Test negative for hepatitis C, or have a positive antibody test followed by a negative RNA test.
• Have adequate heart function.

Exclusion Criteria

• Pregnant or breastfeeding, or planning to become pregnant during the study or within 4 months after the last dose of tobemstomig or pembrolizumab, and 6 months after the last dose of nab-paclitaxel.
• Have poor vein access for treatment.
• Have had another cancer within the last 5 years, except for certain low-risk cancers.
• Have untreated or worsening cancer spread to the brain or spinal cord.
• Have a history of cancer spread to the membranes around the brain.
• Have fluid buildup around the lungs, heart, or abdomen that needs frequent drainage.
• Have high calcium levels in the blood that are causing symptoms.
• Have a history of autoimmune diseases or immune deficiencies.
• Have a history of lung diseases like pulmonary fibrosis or pneumonitis.
• Have active tuberculosis.
• Have significant heart or blood vessel disease within the last 3 months.
• Have an abnormal ECG that is clinically significant.
• Have a history of serious heart rhythm problems or risk factors for them.
• Have had major surgery within the last 4 weeks.
• Have taken certain antibiotics or antifungal medications within the last week.
• Have had a stem cell or organ transplant.
• Have any other serious medical conditions that could interfere with the study.
• Have received a live vaccine within the last 4 weeks.
• Have taken investigational drugs within the last 4 weeks.
• Have previously been treated with certain immune therapies.
• Have taken immune-stimulating drugs within the last 4 weeks.
• Have taken systemic steroids or other immune-suppressing drugs within the last 2 weeks.
• Have a history of severe allergic reactions to certain antibodies or proteins.
• Have known allergies to components of the study drugs.