For people with cancer and HBV who require chemotherapy or another treatment that suppresses the immune system, there is a slight risk that a latent (inactive) infection with hepatitis B can become active again (called reactivation). This is because chemotherapy can weaken the immune system that helps fight infection. It is not known how a latent HBV infection becomes active or causes problems for specific cancers or specific chemotherapy. Some examples of treatment that appear more likely to overwhelm the immune system and lead to reactivation of the infection are the high doses of chemotherapy given before bone marrow/stem cell transplantation and rituximab (Rituxan), a treatment for lymphoma.