A Study of A166 in Patients With HER2-Positive Unresectable or Metastatic Breast Cancer

This study is testing a drug called A166 for people with advanced or metastatic HER2-positive breast cancer who have already received multiple prior treatments. HER2-positive means the cancer cells have a protein that makes them grow faster, and A166 is designed to specifically target those cells. **You may be eligible if...** - You are 18–75 years old - You have HER2-positive breast cancer that has spread or cannot be surgically removed - You have received no more than 5 prior lines of treatment, including at least one HER2-targeting antibody-drug conjugate (a type of targeted therapy) - Your cancer has gotten worse or you could not tolerate your last treatment **You may NOT be eligible if...** - Your cancer does not test positive for HER2 - You have not previously received a HER2-targeted antibody-drug conjugate with a specific type of payload (topoisomerase inhibitor) - You have serious heart, liver, kidney, or other organ problems - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.