Tolerability and Efficacy of Adjuvant T-DM1 in Patients with HER2 Positive Breast Cancer After Incomplete Pathological Response to Neoadjuvant Chemotherapy Including Anti-HER2 Agents.

This study is tracking real-world outcomes in women with HER2-positive breast cancer who receive a drug called T-DM1 (trastuzumab emtansine) after surgery, when their pre-surgery chemotherapy did not fully eliminate the tumor. Researchers want to understand how well T-DM1 works and how well it is tolerated in everyday clinical practice. **You may be eligible if...** - You have been diagnosed with HER2-positive breast cancer - You received chemotherapy plus anti-HER2 treatment before surgery, but cancer cells were still found after surgery - You are receiving or have received T-DM1 as follow-up (adjuvant) treatment **You may NOT be eligible if...** - You are receiving other experimental biological treatments at the same time - You are unable to provide informed consent Talk to your doctor to see if this trial is right for you.