This study focuses on adults who have cachexia (a condition that causes significant unintentional weight loss and muscle wasting) and newly diagnosed metastatic pancreatic cancer (cancer that has spread from the pancreas to other parts of the body) for which they are going to receive initial chemotherapy. The purpose of the study is to evaluate how well an experimental drug called ponsegromab works and whether it might improve health and quality of life compared to a placebo (inactive substance) in patients who have cachexia and metastatic pancreatic cancer. Researchers will evaluate ponsegromab by examining changes in participants’ body weight, physical activity, symptoms, and quality of life. The study will also assess how well the drug is tolerated and its safety. Ponsegromab will be administered as subcutaneous injections (under the skin).