This study is for people with triple-negative breast cancer that has not spread after initial treatment with chemotherapy and pembrolizumab. Pembrolizumab is a type of immunotherapy that helps the immune system fight cancer. The study compares continuing pembrolizumab treatment to just watching (observation) after surgery to see which is better at preventing cancer from coming back.

Participants in the study will be randomly assigned to one of two groups. One group will continue to receive pembrolizumab through an IV (a tube that goes into a vein), while the other group will be closely monitored without additional treatment. Both groups will have regular check-ups, blood tests, and possibly a tumor sample taken for research purposes.

Key Points:

• This study involves regular hospital visits for check-ups and possible treatment.
• Participants must have completed initial chemotherapy and surgery for breast cancer.
• There are no costs to participate, and pembrolizumab will be provided if needed.

People can join if they are 18 or older and meet specific health criteria, and they must not have other serious health issues or be pregnant.