I had Perimeural Invasion, PNI, a number of times found through biopsy. Most were treated with surgery, Chemoradiation, but when it wasn't I had recurrences once to the epidermal layer of skin. Evidence suggests PNI to be a risk of local-regional recurrence, metatastic spread, and reduced survival, although it's not fully understood or sgreed upon. PNI, which is microscopic, is basically unseen by scan, but MRI is used to see the tumor extent, and PNZo is almost always an indication got adjunct radiation like IMRT, but it's uncertain what roll chemo has with PNI.

Sounds like the chemo used was a form of induction chemo, which is used to sensitize the tumor for radiation, reduce the tumor burden for surgery, but time, sometimes eliminating it completely, but this response usually doesn't last, and tumor will likely return in less than a year, and in my case, after a complete response, it did, although my tonsil tumor never did. I'm not sure the intent MD Anderson had, but likely had something to do with the refusal of any surgery. Chemo alone does not cure this not does immunotherapy, although durable responses have been shown.

Surgery is usually the first option with recurrences with or without radiation or Chemoradiation. Not sure why a total glossectomy was recommended if the tumor was still small. With PNI i guess the cancer would need to be removed along the nerve line until the margins are clear.

Small tumors, T1, T2 can sometimes be treated with radiation, but as mentioned, they said no. Maybe with Proton therapy it can, and believe it can with a flap with new tissue, but that involves removal of the tumor.

In absence of surgery, I'm not sure what else can be done curative, except palliativly with more chemo, probably different than used begor or maybe an EGFR Inhibitor like Erbitux, where some are on
maintenance for years, and maybe immunotherapy down the line, as mentioned.

Good luck with everything.