Rita,
I am a recent "Unknown or Occult" Primary. These days most "Unknowns" H&N primaries are found once the patient is referred to a CCC, so true H&N Unknowns are now less the 1%.

First, an intense search is done to locate the primary with extra hi-res scans, scopes, exploratory during ND and Tonsillectomy surgery.

If nothing is found then the location of the Unknown primary is approximated to all potential sites by the location of the cancerous lymph node(s).

The RT treatment fields are kept much wider and the potential primary sites are treated to an intensity that normally might be reserved for just the tumor.