What is your approach to a patient with an advanced stage diffuse large B-cell lymphoma treated with chemotherapy alone (with a PET CR) who then develops an isolated CNS relapse?

This is a challenging albeit relatively rare situation. First, I would make sure to complete systemic workup, including MRI of brain/spine, CSF cytology, and PET/CT. I would not consider radiosurgery even for a single brain lesion, as this is ultimately a more diffuse disease process. If patient has...