Not true. An emergency department in the US is obligated to provide life-saving care, as are EMS services and hospital doctors if the ER doc thinks you have an immediately life threatening condition . But a random oncologist has no obligation to treat you if you have a life-threatening cancer, unless you go to an ER and they determine that your condition is immediately life-threatening (say, a perforated bowel). Then the surgeon will treat you enough that you are not inmediately dying, but they are not obligated to say, remove an underlying cancer if it’s not causing immediately life threatening problems