To those who have or know alot about neurofibromatosis

Hello , 

My dad has neurofibromatosis 1 and also has been battling rectal cancer for the last three years since that time I have searched for info on neurofibromatosis and found some but not much . Now my dad has had a neurofibroma in his throat for the last 20 years . It causes no symptoms so it's never really been much of a concern until his last pet scan 2 months ago . 

      That pet scan showed thickness at the base of the tongue as well as increased uptake on the pet scan . Since it's rare for rectal cancer to spread there we are assuming it's the neurofibroma . So naturally I have been researching the odds of a neurofibroma turning to cancer ? Also is it common for neurofibroma's to turn to cancer at the base of the tongue/throat ? Also if it is a neurofibroma that turned to cancer in his throat whats the prognosis for that ? Can a neurofibroma cause thickness and increased uptake on a pet scan and not be cancer ? 

      I have read alot about nerve shealth tumors and that they can be bad spread quickly is that true ? I don't even know if I am posting in the right place but since neurofibromatosis can turn into a Sarcoma I thought might as well try here . My dad has a appointment with a ENT next week so just looking for any information about neurofibromotasis turning to cancer . The ENT is in the cancer center and sent us paperwork about oncology services so it's making me think they already think it's cancer . So that I am prepared for the appointment with questions and such so if anyone can help me out I would be so grateful .