The figures for an unknown HEAD AND NECK primaries are very very low but for cancer in general they are quite high.

The radiation plan is developed by mapping the nodes with SCC and adjacent nodes in those node chains back to all probable primary drainage sites. Then "fields" were established for the probable primary sites and those fields received Radiation along with the nodes.

MD Anderson CCC has led in the research and development of the treatment protocol for unknown OC primaries and recently found HPV as a major cause, so NCCN guidelines now require testing of the lymph nodes for HPV.