I'm pretty sure that the 30% of occult mets to lymph nodes applies to patients who have had CT scans and physical exams but NOT a neck dissection. That's what my ENT told me when I was diagnosed as stage II but hadn't had the surgery yet. After I'd had the neck dissection, he said my risk of occult mets was much lower and it was clearer I was a stage II, but, since he had only done one side for the neck dissection, there was still some risk it had spread to the other side and I needed radiation on both sides to be sure to eliminate that risk.

But Brian is right that the lymph system isn't the only way cancer spreads. It can spread along nerves and through the blood as well. That's why, even though I had no node involvement after a neck dissection, it was recommended to me that I have rad (and chemo although that was an aggressive recommendation)--because the tumor itself had perineural involvment and also vascular involvement which suggested I was at risk of spread through those alternate routes.

Nelie