This study is designed to test the safety and effectiveness of a new drug called **HDP-101** in people with a type of cancer known as **multiple myeloma**. Multiple myeloma is a cancer that affects plasma cells in the blood. Participants will undergo two parts in the study: dose escalation and dose expansion. The first part will find the right dose, while the second part will see how well the drug works and confirm its safety.
Key Points:
- Length and Visits: The study includes multiple parts and may require several visits and tests.
- Eligibility: Adults (18+) with specific cancer history and previous treatments are eligible.
- Risks: Some may experience side effects, and those with certain conditions cannot participate.
Eligibility criteria include having had certain treatments before and being in good enough health to participate. Some conditions, like liver disease or recent treatments, may prevent joining the study. This study is important for finding new treatments for multiple myeloma and other plasma cell disorders.