A Study of XMT-2056 in Advanced/Recurrent Solid Tumors That Express HER2

This study tests XMT-2056, a new antibody-drug conjugate, in patients with advanced or metastatic solid tumors that are HER2-positive (meaning the cancer cells have high levels of a protein called HER2 on their surface). It is an early-phase study to evaluate safety and find the right dose. **You may be eligible if...** - You have been diagnosed with a solid tumor that has come back or spread and tests positive for HER2 (IHC 3+ or IHC 2+ with positive ISH test) - You have received prior standard treatments and your cancer has continued to progress - You are in good general health (ECOG 0 or 1) - You have measurable tumors that can be tracked on scans - You are willing to provide a tumor biopsy sample **You may NOT be eligible if...** - Your tumor is HER2-positive only through gene mutation or amplification without the IHC/ISH positivity criteria - You have uncontrolled brain metastases - You have significant lung, heart, or kidney problems - You are pregnant or breastfeeding - You have received prior treatment with this specific drug Talk to your doctor to see if this trial is right for you.