This is a thing that I sort of find weird, you all do know that people survive having cancer all the time? This would be especially true of a doctor, like Jane is, that would have been doing her own self examinations. I always found it weird that the cancer got as bad as it did considering that Jane should have caught the cancer way before it would have been fatal. Maybe she had a death wish and wasn't doing her self exams? Hel, that might even be the reason she refused a magic treatment for her magic cancer.
And before anyone jumps on me for being disrespectful to cancer patients by suggesting that they might live through cancer, my own mother died from cancer the same day Jane did. I read issue #705 in the funeral home during the viewing. She'd nearly died of the cancer twenty years before, beat it, and then it came back. People don't just automatically die of cancer.