Didn't have cancer, but had a career-ending running injury that crippled me at age 20. Walked with a pronounced limp for some years.
I've never been able to run since, but eventually was able to walk 50km in a little under 11:00/mile. I can't say I really enjoyed that--it wasn't a physical pleasure, the way running was--but, with time, I developed more appreciation for what I *could* do and less regret about what I couldn't.
As far as the anemia: that'll probably get better, and your running will feel a ton better when it does. While you're waiting for that, my suggestion is not to make all of your running slow, just so you can say you "ran" the whole three (or five, or two--whatever) miles. Instead, at least once or twice a week you should just go for a mix of running and walking:
Just run for, say, 10 or 15 seconds; walk the rest of the minute; and repeat. The running shouldn't be sprints, but for 10-15 seconds it should be possible to go at something like a normal *running* pace/motion. This will feel a *lot* better than the slog-and-jog that you're presently limited to on your continuous runs.
Good luck.