This study looks at **triple-negative breast cancer** (a type of breast cancer that doesn't have certain receptors) in patients who had a *pathologic complete response* (no signs of cancer) after getting chemotherapy and **pembrolizumab** (a medicine that helps the immune system fight cancer). Researchers want to see if just watching patients (observation) after surgery is just as effective as giving them more pembrolizumab.

Patients will be randomly placed in one of two groups: one will receive more pembrolizumab, and the other will watch for any signs of cancer returning. Both groups will have regular check-ups, including blood tests and biopsies (taking a small sample of tissue for testing).

• The study requires patients to have regular visits for check-ups and tests to monitor their health.
• Participation in the study could help researchers find better ways to treat this type of cancer.
• Those in the pembrolizumab group may experience side effects, while the observation group will not receive additional medication.

To join, patients need to meet specific health criteria and be willing to provide tissue samples. This study is not for those who have stage IV cancer or who cannot follow the study plan.