Entecavir Prophylaxis for Hepatitis B Reactivation for CD20 Positive B-cell Lymphoma Patients With Resolved Hepatitis B (Negative Hepatitis B Surface Antigen, Positive Hepatitis B Core Antibody)

This study tests whether taking an antiviral drug called entecavir preventively can stop hepatitis B from reactivating in people with B-cell lymphoma who are treated with a type of therapy (anti-CD20 medications like rituximab) known to wake up dormant hepatitis B infections. These patients have past (resolved) hepatitis B but are at risk when their immune system is suppressed. **You may be eligible if...** - You have been diagnosed with CD20-positive B-cell lymphoma - You are about to start first-line lymphoma treatment containing an anti-CD20 antibody (like rituximab) - Your blood tests show past hepatitis B exposure (negative surface antigen, positive core antibody, no detectable virus currently) - Your liver function is adequate **You may NOT be eligible if...** - You currently have active hepatitis B (positive surface antigen or detectable virus) - You have had prior chemotherapy or radiation for lymphoma - You have other liver diseases (hepatitis C, autoimmune hepatitis, cirrhosis) - You are pregnant or breastfeeding - You have HIV or a history of immune deficiency Talk to your doctor to see if this trial is right for you.