He looks good. I did the same thing but due to stomach cancer which made it a lot harder as I am 15 years his senior I imagine.
Regardless how weight loss happens - assuming you’re not under conditions of extreme privation - it’s usually a good thing. Try to look at it that way and stay mobile, engaged with life, and at least mentally, if not physically, active. Try to trust your doctors but look things up on your own (not just on the interweb but in the library).
Not assuming you didn’t already beat your cancer - these are just ideas I have developed while working in health care and observing cancer cases. You’re still here after that much weight loss, so that’s a good sign! Maybe you’ll make it a while longer. At least your golf swing will get better!