If he thinks that he have cancer and he is going to die but everything is ok? what is this? also he claims to have clogged throat.

Sounds like severe: Anxiety. Hopefully this person is following up with his primary care doctor to help him through this difficult time.

Mental illness: This is abnormal behavior -- I'm going to assume that this person claims to have cancer, appears well, and also professes indifference, and also to claim to have a throat issue but breathes, eats and drinks normally. Suggest nicely that perhaps a physician could help, or perhaps there's a mistake. Don't try to understand people, and don't try to cure this individual.

See a psychiatrist: Health phobia also called hypochondria. It is excessive worrying about your health. Hypochondria is among the most difficult and most complex psychiatric disorders to manage. See a psychiatrist.