 One of those cancers is triple negative breast cancer. Keytruda may be used with chemotherapy medicines as treatment before surgery and then continued alone after surgery when you have early stage breast cancer and are at high risk of it coming back. Keytruda can cause your immune system to attack healthy parts of your body during or after treatment. This may be severe and lead to death. See your doctor right away if you have cough, shortness of breath, chest pain, diarrhea, severe stomach pain, severe nausea or vomiting, headache, light sensitivity, eye problems, irregular heartbeat,