Circulating Tumor DNA in Primary Mediastinal Large B-cell Lymphoma (PMBL)

This study is investigating whether traces of cancer DNA floating in the bloodstream (called circulating tumor DNA, or ctDNA) can help doctors monitor how well treatment is working in people with a rare type of chest lymphoma called primary mediastinal large B-cell lymphoma (PMBL). Blood tests may one day replace or reduce the need for scans. **You may be eligible if...** - You are over 18 years old - You have been newly diagnosed with primary mediastinal large B-cell lymphoma confirmed by biopsy - Your disease involves the area in the middle of the chest - You have not started treatment yet (except for a short course of emergency steroids) - You are planned to receive standard chemotherapy with rituximab **You may NOT be eligible if...** - You have received prior treatment for this lymphoma (beyond emergency steroids) - You have another active cancer - You are unable to consent or comply with the study schedule Talk to your doctor to see if this trial is right for you.