Hi, Thanks for writing in. A thorough clinical evaluation of his cancer is required to know the probable cause of his neck pain. It is suspected that he might be weak, have an infection in the neck region or the cancer itself is in the neck. Pinching of nerves from the cervical spine also causes pain that might be severe. If the pain is of sudden onset then please have him examined by the treating doctor and then get an opinion from the orthopedic surgeon if required. A physiotherapy session might help to ease his movements and this facility might be sought at the hospital where he is admitted. Please do not worry.