How fast it drips in depends how fast the person needs the blood. Other specialities like medicine or pediatrics take less time. The best way to prevent cancer is to exercise, eat a good diet and never smoke. I am trying to invent a new approach where we could put a tiny catheter through the nipple into the breast and squirt something down the duct and just wash the cancer away. It will be great if it works.
All cancer is screwed up genes.
Sometimes you inherit the screwed up gene from your mother or father and sometimes you inherit normal genes and something comes along in the environment and screws up the genes. But in the end it is all screwed up genes so that the cells don't grow right. It is very hard. But we are not perfect. It is much easier to give people good news.