Put simply, when you go to the ER and if it is an emergency, they treat it and then release you to follow up with an specialist or doctor for further treatment.
The problem with cancer, is that even though they handled with surgery and let go, is that most likely this person will need chemo, radiation or more surgery (not emergency), thus the care will be continuous for months/year to either be cancer free, or given more time to live.
Cancer is expensive, and could cost over a MILLION or more to treat, and that could be just chemo or radiation and not surgery. A close friend of mine, her husband has lung cancer and has been treating for over a year, and to date, the cost is 2 MILLION dollars that insurance has paid for.
So, most doctors/hospitals with that kind of expenses will not treat, since it is one thing to "write off" maybe $25,000 to $50,000 for emergency treatment, but will not for millions.
So, poster Judith is correct, can apply for disability and depending on the disability may qualify for Medicaid or even Medicare to pay for ongoing treatment.