Dealing with a cancer is way beyond my challenges. Like you I really dislike prescription pain meds and I'm taking Ibuprofen. For some reason pain has never been the challenge with me. Losing conditioning that I might never get back, vs going to far and damaging something is my main concern.
I upped my pace yesterday, and tried a compression shirt which helped a lot but hurt so much taking off that I'm seriously thinking about cutting one side and sewing in a velcro strip. Heart rate when I finished 5K was 20 beats higher than after a normal steady run which would also be a mile further as well as 90 sec/mile faster. And more out of breath yesterday which is concerning So it feels almost like starting over, tho I'm still hopeful that it's more about healing than the endurance.
Nothing inherently wrong with running slower though, or cycling slower when the time comes. But will the end results differ - it's one reason why this thread. Also the obviously reduced lung capacity, can it be brought back and the optimal method. Other than the inhaler toy they give you for deep breathing practice - I think that it can only go so far and moderate to strenuous exercise has to be more effective.