Exactly how or why primary central nervous system lymphoma occurs in the body is not well understood. In addition, the most significant risk factor for this disease, a compromised immune system, cannot be easily addressed. Therefore, there are no known ways to prevent primary central nervous system lymphoma. It is interesting, however, that the incidence of this cancer in persons with HIV has decreased since the widespread use of medications to treat HIV. Whether measures to strengthen a person's immune system (such as the use of antiretroviral medications to treat HIV) can prevent primary central nervous system lymphoma remains to be seen.