They do not know the prognosis at this time, everyone responds different to treatment. I was told point blank to my face there is no cure for my lung cancer DNA Gly12Asp. I have been on Keytruda for 4 years due to recurrence 4 months after surgery, so far scans look great. Don't be afraid to ask the questions if your father is okay with it then ask even write them down and take it with you. You are his support system so ask the questions. I will be going off Keytruda and they will not tell me remission or cured he said he don't know, which is an honest answer, cancer is a fickled disease. I wish him well you to