I asked that same question when I was initially diagnosed and my head & neck surgeon informed me that the tumor had been there about 2 years. It had grown to 6 cm, and was chokinng me when I would sleep at night. I suspect that my tumor was HPV induced and it was also a polypoid tumor (simliar a polyp like found in colon cancer) so your fathers tumor may have different growth characteristics.

It can be shrunk with radiation. My tumor completely dissapeared after only 3 weeks of radiation.

You may wish to revisit this with a risk/benefit assessment, even if from a palliative care standpoint, with a Radiation Oncologist. Ofterntimes radiation is administered to mitigate pain and it can also prolong life as well.