I was diagnosed in August of 2019, had a bi-lobectomy in 2020, recurred in 2020 4 months later, did immunochemistry test for PD-L1 pos for 85%. so was put on Keytruda late 2020 have been on it ever since. No recurrence yet but may be stopping treatment due to they do not know if I am getting any benefit from it still. So, I guess one way to find out is to discontinue for a while and follow up every 6 weeks and CT scan or PET/CT every 3 months. I am scared but I have lived this long, thankfully.