That's a rather general thing Bee - does he mean stuck in the back of his neck or he has a stiff neck or he feels there is something stuck in his throat????
It is important to remember that not everything that happens to him is going to be due to the cancer. Depending on the previous questions, has he changed his pillows recently or slept awkwardly? Are any of the spinal mets at the top of his spine or are they all lower back? Are his lymph glands swollen in which case has he got a temperature and possibly a throat infection?
Perhaps most important, can he swallow normally? If in doubt, phone GP or NHS direct for advice.