I think all cancers are deadly! For example, lung cancer kills most people, breast cancer is most common in women, pancreatic cancer has the lowest chance of survival.
Cancer starts of as a small tumour and if found at that stage most of them are treatable at that stage. However as it grows bigger, and spreads it starts affecting basic functioning of the body and then it doesnt matter what type of cancer it is. It becomes very hard to treat and fatal.