You might be able to get ER treatment for when the cancer throws a clot and causes a stroke or infarction, but somehow I'm guessing that ERs don't perform chemotherapy and radiation for people who can't pay. Am I wrong on that? Do ERs perform chemotherapy?

Public hospitals, for instance, are required to provide indigent/uncompensated care.

Definitely, which means that hospitals soak up a lot of uncompensated E.R. costs associated with people whose long term health issues are not being treated. Those hospitals are not required to actually provide that long-term care, e.g. chemotherapy regimens. (Unless you're saying they are, which would be happy news to me, since I understood the situation to be a lot bleaker than that for the uninsured.)