This study is testing a new treatment for people with **metastatic solid tumors** that have a specific gene problem, called **MTAP deletion**. Metastatic means the cancer has spread to other parts of the body. The MTAP gene helps cells grow, and when it's missing (or deleted), it can cause problems. **BMS-986504** is a special medicine that might help stop cancer cells from growing by blocking certain enzymes. **Pemetrexed** is another medicine that helps by stopping cells from using a vitamin called folic acid to make DNA, which can kill tumor cells. **Key Points**: - **Study Length**: Treatment cycles are 21 days long, with follow-ups for up to 12 months. - **Visits and Tests**: Patients will take medicine, have blood tests, and get CT scans during the study. - **Eligibility**: Patients must be 18 or older, have specific cancer types, and meet health requirements. Participating in this study involves taking medicine, having regular check-ups, and meeting specific health criteria. It’s important to understand the potential risks and benefits before joining.