Sintilimab Plus Rituximab Followed by R-CHOP Regimen in Untreated PMBL

This study tests whether adding an immunotherapy drug (sintilimab, a PD-1 inhibitor) to rituximab before starting standard R-CHOP chemotherapy can improve outcomes for people newly diagnosed with primary mediastinal large B-cell lymphoma (a type of lymphoma that starts in the chest). **You may be eligible if...** - You are between 18 and 75 years old - You have been newly diagnosed with primary mediastinal large B-cell lymphoma (confirmed by biopsy) - You have not yet received any treatment for this lymphoma - You are in good physical condition (ECOG 0–2) - Your expected survival is more than 12 months - Your organ function is adequate **You may NOT be eligible if...** - The lymphoma has spread to the brain - You have previously received immunotherapy drugs like PD-1 or PD-L1 inhibitors - You have active autoimmune disease requiring systemic treatment - You are pregnant or breastfeeding - You have HIV, active hepatitis B or C - You have had another cancer in the past 5 years (with some exceptions for treated skin cancers) Talk to your doctor to see if this trial is right for you.