Viscum Album for TNBC on Adjuvant Pembrolizumab

This study is testing whether adding Viscum album (mistletoe extract) to standard treatment for triple-negative breast cancer (TNBC) can improve outcomes. Participants will receive their regular chemotherapy and the immune checkpoint inhibitor pembrolizumab, plus either mistletoe extract or a placebo. **You may be eligible if...** - You are 19 or older - You have been confirmed to have triple-negative breast cancer - Your cancer is localized (not spread to other organs) - You have completed surgery and radiation, and are starting or have recently started chemotherapy with an immune checkpoint inhibitor - Your blood counts and organ function are within acceptable levels **You may NOT be eligible if...** - Your cancer has spread to other parts of the body (metastatic) - You have uncontrolled infections or autoimmune conditions - You are pregnant or breastfeeding - You have had prior systemic therapy for this cancer Talk to your doctor to see if this trial is right for you.