I did a MedLine search for this, as it is not that common in head and neck cancer patients. I found numerous articles and the most through I think is this one http://www.emedicine.com/emerg/topic260.htm

When you read it you will see that while a possible pronosticator of a malignancy, there are a variety of other less dire things that can bring it about. Differential diagnosis, which brings an answer by exploring all the possible signs and symptoms, will point a diagnostitian in one direction or the other. While a lot of the details that come to mind after researching this are not included in your original post, I think that the thing most telling to me from what is there, is that your oncologist (who would certainly be doing other diagnostic tests on you to look for second primary maliganancies in your lungs etc. if he thought this a serious concern) is sending you to an endocrinologist instead. A hyperthyroid situation would be in that person's knowledge base, and it is perhaps your oncologist's perception from your most recent exams and diagnostic tests (you don't mention what you have been through) lead him to believe that malignancy is NOT the most likely differential diagnosis. Like all of us that are survivors, when some part of our blood work, or a small spot on one of our scans appears, the survivor's mind immediatley goes to the C word. Welcome to the world of survivorship. I do this when I get a toothache or more recently when a small dark spot appeared on a scan that included my liver, which turned out to be nothing more than a grouping of capillaries, or a hemangioma. I would put a call in to your oncologist and ask him what his thinking/reasoning is; what he thinks the possible differential diagnosis list might have on it. He may have ruled out the really bad, and is just ensuring that the other possible causes are dealt with properly.