Approximately 90% of primary and secondary CNS lymphomas are diffuse large B-cell lymphomas, with the minority made up of T-cell lymphomas, Burkitt lymphomas, and low-grade lymphomas. Primary CNS lymphoma is highly associated with HIV, and is the second most common cause of brain mass lesion (CNS toxoplasmosis is first) in patients with coexisting late-stage HIV and CD4 + T-lymphocyte count of <50 cells/𝜇L. Though CNS lymphoma is more common in men than in women with an average age of diagnosis of ~55 years, patients with coexisting AIDS are usually diagnosed at a much younger age of ~35 years. The Epstein–Barr virus (EBV) is found in ~99% of patients with AIDS-related primary CNS lymphoma, while found in ~90% of the general population. Patients with EBV + primary CNS lymphoma have a poorer prognosis than EBV patients as the EBV genome has been found to express anti-apoptotic genes in its genome, leading to malignant transformation of cancer cells.