Same as a friend of mine lasted. Doc gave him 9 months.
EDIT: and I think he was lying a bit about the diagnosis in that letter, or else his docs were lying a bit to him. That may have been what he wanted to believe. If it was discovered "routinely" outside of surgery it was stage 4 to begin with, and there wasn't any hope, and it was probably inoperable (the fact that he got an operation and only lasted 12 months suggests the op didn't do any good).
Not really casting aspersions on him, though, just cancer is really shitty, and this one particularly bad.
http://www.nintendo.co.jp/ir/en/stock/meeting/140627/