How long has it been since he was told or you found out about the prognosis? Denial is natural and since it is he, and not you, let him go through this......but for only so long.
In any case, as lilymadeline says, get a second opinion and a third if you want. Doctors can be wrong, can give the worst possible scenario (because they feel that is best) and there can be all sorts of reasons. See another doctor, from a different hospital for your own and your husband's peace of mind. Think of it as comparison shopping. It never hurts to see if you are missing something.