Lymphoma is cancer of the lymphatic system, a network of lymph nodes, organs (including the spleen, thymus, and tonsils), and vessels that help make up the immune system. There are many different types of lymphoma, and they can be divided into two categories: Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL). The major difference between the two is the type of cells involved.
Generally speaking, HD is easier to treat than NHL. Lymphoma is easiest to treat in its early stages, when the cancer hasn't spread beyond the lymphatic system. Lymphoma that either spreads to the bone marrow or develops in the brain can be more difficult to treat.
HIV-infected people are at a slightly higher risk for developing NHL than non-HIV-infected people. NHL can also progress (get worse) faster in HIV-positive people and can be more difficult to treat. It is not clear if HIV-positive people are at a higher risk for developing HD. However, HD does occur in HIV-infected people and, because of underlying immune suppression, can progress faster and may be more difficult to treat.
A number of recent studies have found that fewer HIV-positive people are being diagnosed with lymphoma today than they were in the years before combination anti-HIV drug treatment became available. The risk of developing one of the more serious types of lymphoma – lymphoma of the brain (primary CNS lymphoma), for example – has dramatically decreased in recent years. However, some types of NHL – Burkitt's lymphoma, for example – have not decreased.
Lymphomas are more likely to occur in HIV-positive people with fewer than 200 T-cells; primary CNS lymphoma is more likely to occur in people with fewer than 100 T-cells. However, there have been reports of lymphoma occuring in HIV-positive people with higher T-cell counts.
While the cause of lymphoma is still not known, many researchers believe that environmental toxins – such as pesticides – can cause this form of cancer. The Epstein-Barr virus (EBV) has also been found to play a role in the development of lymphomas, particularly in HIV-infected people.