This randomized phase III trial studies how well pembrolizumab works in treating patients with triple-negative breast cancer. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with...

This randomized phase III trial studies metformin hydrochloride to see how well it works compared to placebo in preventing breast cancer in patients with atypical hyperplasia or in situ breast cancer. Chemoprevention is the use of certain drugs to keep cancer from for...