- For Cohort 2, CT or MRI within 14 days prior to start of study drug. MRIs should include vascular imaging when possible. For Cohort 2, corticosteroid dose must be stable or decreasing for at least 5 days prior to the scan. If steroids are added or the steroid dose is increased between the date of the screening MRI or CT scan and the start of treatment, a new baseline MRI or CT is required. For Cohort 1 subjects, CT or MRI should be performed ideally within 14 days prior to study registration, but because the screening MRI for this subset of subjects will not be used for evaluation of response, it is acceptable for this MRI/CT to have been performed greater than 14 days prior to registration if unavoidable. Furthermore, for this same reason, fluctuation in corticosteroid dose around this MRI does not warrant repeat scan so long as there is documented unequivocal evidence of tumor progression available.