Michael Douglas Has Oropharyngeal Cancer

Michael Douglas announced he has"stage IV throat cancer" on late night TV this week.  Any announcement of cancer causes people to stop and take a deep breath but the idea of throat cancer is particularly scary.  So what exactly is throat cancer?  How is it diagnosed and treated? 

The clinical term is oropharyngeal cancer that involves the base of the tongue, the mouth, the tonsils, or the front