Nicole, I am so sorry to hear of your Dad's diagnosis. You are right about it being extremely rare, I looked on the internet for info, and found this site, it may give you more information than you want at this point, but it is well explained and fairly easy to read.
http://www.emedicine.com/orthoped/topic531.htm
It is sometimes a secondary effect of radiation therapy to the area, so there may be a few folks on this board who have experience with this problem. I have not, so cannot offer anecdotal advice. I do offer my best wishes for your Dad's speedy recovery.
Andrea

SCC L lat tongue,Dx 9/15/05 T1N0MX L MND and L lateral hemiglossectomy 10/03/05. Recurrence 11/15/06 2nd surgery 12/04/06 hemiglossectomy 3rd surgery 01/15/07 tonsillectomy Radiation 01/25/07 to 03/08/07 3-D/CRT X 30