I had an MRI on Wednesday, and discussed the results with my oncologist today. The previously enlarged lymph nodes continue to be normal, and the tiny liver thing is exactly the same. At this point, he thinks it might just be some random scar. There has been no change at all since April 2019. My onc actually used the "R" word: remission.
The upshot, we will stop Keytruda, and scan every three months. Hope that my arthralgia fades, the rapidly the better, which will help me get exercise and manage my T2 diabetes again, and live a normal life.
I'm a happy camper. And realize how lucky I am.