For metastatic NSCLC patients with mixed response to pembrolizumab, would you radiate focal progressing lesions and continue pembrolizumab, add in chemotherapy to pembrolizumab, or discontinue pembrolizumab and move to second line?  

These are all reasonable approaches.  The better and longer the prior response to pembrolizumab and the more limited the # of progressing sites, the more likely I would be to consider radiating those sites and continuing pembrolizumab alone. I have not yet added chemotherapy to pembrolizumab, ...