My mom had Whole Brain Radiation for multiple mets to the brain from lung cancer ( EGFR + exon 19 and T790 M negative) that ended two months ago. She was started on Tagrisso as first line therapy due to some evidence of leptomeningeal disease. Unfortunately she has now developed symptoms suggesting interstitial lung disease and she is now off of the Tagrisso. She responded well to the drug both in the brain and the lung after just six weeks. My question is since she is now off of the drug, how long do we have until progession of disease develops again in the brain.