How To Treat Throat Infection On Being Diagnosed With Tonsil Cancer?

Three years ago my father was given a clean bill of health after treatment for Stage 3 tonsil cancer. In the last few weeks he has experienced a throat infection, which caused massive swelling and left him unable to breathe and swallow. The hospital performed a tracheotomy and conducted a biopsy of his lymph node. The biopsy found massive necrosis, along with some cancer cells. He is now scheduled for a PET scan, but the oncologist says he isn t concerned. In all honesty, is his cancer back? It would make sense that it has returned. I just need an honest answer.