Effects of MK-3475 (Pembrolizumab) on the Breast Tumor Microenvironment in Triple Negative Breast Cancer

This study is testing whether an immunotherapy drug called pembrolizumab (also known as Keytruda) can help the immune system attack early-stage triple-negative breast cancer — a type that does not respond to hormone-based treatments — before surgery. **You may be eligible if...** - You are 21 years of age or older - You have been diagnosed with invasive triple-negative breast cancer (a type that is negative for estrogen, progesterone, and HER2 receptors) - Your tumor is 3 cm or smaller and in one location - You have not yet had surgery or chemotherapy for this cancer **You may NOT be eligible if...** - You have had prior chemotherapy or radiation therapy for breast cancer - You have cancer that has spread beyond the breast or nearby lymph nodes - You are pregnant or breastfeeding - You have a serious autoimmune disease or are on immune-suppressing medications - You have other significant health conditions that could interfere with treatment Talk to your doctor to see if this trial is right for you.