To throw another reference into the discussion, section 1.8 of McKinnell et al.'s The Biological Basis of Cancer spends a few pages on this. Summary: cancers can cause organ failure, but because the body has "an enormous reserve of normal tissue plus a built-in mechanism to regenerate more" organ failure is not usually the proximate cause of (edit: non-leukaemia) cancer death; the most common cause of death is instead cachexia (wasting) and hence infection.