T4 is based on size, it may or not have spread -- if it started on the tonsil (common, esp. with HPV+ tumors) it might well spread to the base of tongue. It may be moderately, well or poorly differentiated, that is based on the cellular appearance in the pathology exam.

Well-differentiated means the cells are still close in appearance to the normal tissue type, with more-or-less normal nuclei and mitotic figures -- and poorly differentiated have a lot of abnormalities -- multiple nucleii, perhaps no nucleii, abnormal mitotic figures, etc. The "rule of thumb" is that these latter cancer cells are more able to invade other tissue types, while those which still well-differentiated have problems living outside their originating tissue. However, many HPV+ cancers (which usually present first in tonsil and/or base-of-tongue) are poorly differentiated and these actually seem to have a better prognosis, and respond better to treatment (per recent studies). My husband Barry's cancer was moderately-well differentiated, but strongly HPV+, so there is obviously variation.

If the radiation plan delivered the usual 66 cGy (or above) to the nodes then they should respond as well as anywhere else, per our ROs.

His MO and MO (and ENT) did not recommend additional surgery just to check the nodes -- it would have been done only iff his first PET/CT scan had revealed residual disease.

Gail