My dad was diagnosed w/ stage IV NSCLC, EGFR+ in January 2016. He was in a clinical trial for a 3rd gen TKI drug up until last month when a progression was found in his liver, and he developed much more pain in his chest, back and leg, probably due to bone metastases. Not finding a T790 mutation, his doctor switched him to Tarceva. How long can we reasonably expect before there will be any effect? How long does it usually take before the drug starts to shrink the tumors?