This study aims to find out how well a new medicine, called golcadomide, works and how safe it is when combined with a standard chemotherapy treatment called R-CHOP. R-CHOP stands for rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone. The study will compare this combination to a placebo (a substance with no active ingredient) plus R-CHOP in patients who have never been treated for a certain type of cancer called high-risk large B-cell lymphoma (LBCL). LBCL is a cancer of the lymphatic system, which is part of the body's immune system. The study includes people with different types of LBCL, like diffuse large B-cell lymphoma (DLBCL) and others with specific cell changes.

• Participants need to have untreated high-risk LBCL with specific characteristics.
• The study involves taking the medicine and going for regular check-ups and scans.
• Some people may not qualify if they have other health issues or different types of lymphoma.