There might be solutions for planned hospital stay/procedures, it depends on a state you are in. First, find if your state has a program. Then find a hospital that participates in it. They will require proof of income; if your income is less then certain threshold, it may be free for you; above it, you may have to co-pay some portion according to sliding scale. For office visits, I haven't heard of any public assistance programs. But I've seen people walking to the receptionist and telling "I do not have insurance", they are not turned away. In smaller practices, you have to negotiate your pay. If you are not confident with negotiation, you may want to search for a "non-profit" hospital and look for an MD that work in their "medical org/group/network". They might have appropriate policies. I've seen charges slashed by 70% which bring it to what the office would get reimbursed by insurance, in average. So, it looks quite fair. Hope this helps.
Are you saying for cancer treatment? That is a tough one. Most hospitals will not treat cancer without insurance. Legally no hospital has to. They only have to treat you if you come into a ER bleeding to death. There are local doctors in our area who will treat breast cancer for women without insurance. They volunteer the surgery. I do not know how you would find that out may be the local chapter of the Cancer Society.
Alex