Sequencing Antibody Drug Conjugates in ER+/HER2 LOW/ULTRA LOW MBC

This study is looking at the best order (sequencing) to give two types of targeted drug therapies — called antibody-drug conjugates — in patients with advanced breast cancer that is hormone receptor-positive and has low or very low levels of the HER2 protein. **You may be eligible if...** - You are 18 or older - You have metastatic or advanced breast cancer that cannot be surgically removed - Your cancer tests positive for hormone receptors (estrogen or progesterone) and has low or very low HER2 expression - Your cancer has continued to grow despite hormone therapy - You have received prior chemotherapy for metastatic disease **You may NOT be eligible if...** - Your cancer is HER2-positive at a standard level - You have certain serious heart, liver, or lung conditions - You have active brain metastases Talk to your doctor to see if this trial is right for you.