- History of known leptomeningeal involvement (lumbar puncture not required) - Previous stereotactic or highly conformal radiotherapy within 3 weeks before the start of dosing for this study. Note the stereotactic radiotherapy field must not have included the brain index lesion(s) - Brain lesions >3 lesions which were previously treated with SRT - Brain lesion size > 3cm 3. Medical History and Concurrent Diseases a) History of whole brain irradiation b) Subjects with an active, known or suspected autoimmune disease c) Subjects with major medical, neurologic or psychiatric condition who are judged as unable to fully comply with study therapy or assessments should not be enrolled d) Any concurrent malignancy other than non-melanoma skin cancer or carcinoma in situ of the cervix. For any prior invasive malignancy, at least 5 years must have elapsed since curative therapy and patients must have no residual sequelae of prior therapy e) Cohort A (asymptomatic): The use