FIG 4. Response obtained in the treatment of a 67-year-old patient with a primary CNS lymphoma (patient 2). Before study accrual, the patient had been treated with high-dose intravenous methotrexate and radiation and had not responded to these modalities. A, Axial T1-weighted brain MR image obtained at study accrual in April 2001. The highly and homogeneously left frontal enhancing lesion is obvious, as well as the surrounding vasogenic edema. A mass effect is produced on the ipsilateral ventricle, as well as on the gyri. B, Axial T1-weighted brain MR image obtained before the 10th cycle, in April 2002. The tumoral nodule has completely receded, and presence of left frontal encephalomalacia and a vacuum effect on the left frontal horn translate the decrease in mass effect.