Study of GVV858 as a Single Agent or in Combination With Endocrine Therapy in Patients With HR+/HER2- Breast Cancer and Other Advanced Solid Tumors

This early-phase trial is testing a new drug called GVV858 — alone and combined with hormone therapy — in people with HR+/HER2-negative advanced breast cancer and other solid tumors with certain genetic changes. **You may be eligible if...** - You are 18 or older - You have HR+/HER2-negative advanced breast cancer that has progressed on at least one hormone-based therapy combined with a CDK4/6 inhibitor, plus at least one additional treatment line - Or you have another advanced cancer with a CCNE1 gene amplification (Phase I) - Or you have metastatic castration-resistant prostate cancer - No further standard therapy is available or appropriate for your disease **You may NOT be eligible if...** - You have not yet tried required prior therapies - You have received more than 3 prior treatment lines for metastatic disease (for expansion cohorts) - You have serious organ dysfunction or active brain metastases - You have neuroendocrine features in your prostate cancer Talk to your doctor to see if this trial is right for you.