GB1211 and Pembrolizumab Versus Pembrolizumab and Placebo in Patients With Metastatic Melanoma and Head and Neck Squamous Cell Carcinoma

This study is testing whether adding GB1211 (a drug that blocks adenosine, a molecule that can help tumors hide from the immune system) to the immunotherapy drug pembrolizumab improves outcomes for people with advanced melanoma or head and neck cancer. **You may be eligible if...** - You have unresectable or metastatic melanoma (including rare types like mucosal melanoma) - Or you have recurrent or metastatic head and neck squamous cell carcinoma - You have not been previously treated with pembrolizumab or similar immunotherapy for advanced disease - You have good general health (ECOG 0–1) **You may NOT be eligible if...** - Your cancer has spread to the brain (unless stable and not requiring treatment) - You have active autoimmune disease requiring medication - You have had a liver transplant - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.