TReatment of ADC-Refractory Breast CancEr With Dato-DXd or T-DXd: TRADE DXd

This study (TRADE DXd) tests two antibody-drug conjugates (ADCs) — dato-DXd and T-DXd — in patients with HER2-low or HER2-negative (HER2-0) metastatic breast cancer whose cancer has already stopped responding to a prior ADC (a type of targeted therapy that delivers chemotherapy directly to cancer cells). The study aims to find out which ADC works best after another one has failed, helping identify the best treatment sequence for this type of breast cancer. **You may be eligible if...** - You have invasive breast cancer that is advanced or has spread and cannot be surgically removed - Your breast cancer is HER2-low (IHC 1+ or 2+/non-amplified) or HER2-0 (IHC 0) — confirmed on any prior tumor sample - You have previously received an ADC (antibody-drug conjugate) for your breast cancer - Your hormone receptor status (ER/PR) can be positive or negative - You have measurable disease on a scan **You may NOT be eligible if...** - Your cancer is HER2-positive (IHC 3+ or amplified) now or at any point in history - You have not had prior ADC therapy - Your organ function does not meet minimum requirements - You have active uncontrolled brain metastases Talk to your doctor to see if this trial is right for you.