How I treat PCNSL. In the diagnostic work-up, an MRI of the spine (± gadolinium) may be useful if warranted by neurologic symptoms or if CSF analysis is contraindicated. Ultrasonography of the testes is indicated for older male patients with CNS involvement of lymphoma in which testes coinvolvement is suspected on clinical and/or radiographic grounds. The value of a positron emission tomography scan in this setting is not established. Although the schedule of Decadron taper should be individualized for each patient, we recommend a planned taper to be completed within 2 to 3 weeks of diagnosis, between the first and second courses of HD-MTX. Therapeutic options for indolent lymphomas that involve the CNS or dura include rituximab, fludarabine, involved-field irradiation, and HD-MTX for CNS involvement of chronic lymphocytic leukemia/small lymphocytic leukemia. For newly diagnosed patients who are not candidates for HD-MTX, in most cases we recommend a trial of temozolomide and rituximab and/or strategies that use high-dose chemotherapy, before consideration of using whole-brain irradiation. ASCT, autologous stem cell transplant; CR, complete response; EA, etoposide-cytarabine; HSV, herpes simplex virus; MT-R, combination HD-MTX, temozolomide, and rituximab (rituximab is omitted for T-cell lymphomas); PCP, Pneumocytis jiroveci pneumonia; PD, progressive disease; PR, partial response; SD, stable disease; WBRT, whole-brain radiotherapy.