Seda,
I'm certainly no expert but I believe Muceopidermoid Carcinoma prognosis is more a matter of the diagnosed 'grade', not the TNM staging.

Yours has been diagnosed as High Grade with Perineural invasion meaning the cancer is though to be invasive and has already invaded near by nerves.

I'm not sure where you are being treated, but if it isn't a top notch major CCC you might want to consider a second opinion from one.

I am assuming you have Muceopidermoid Carcinoma of the salivary glands and I would think you are wise have the radiation due to the perineural invasion, but that is question best answered by an expert CCC team.

In my opinion, when it comes to fighting this beast anything that gives you an additional 20% bump in your odds is worth taking and most of us get through radiation therapy just fine.

Please see the following reference info:
http://oralcancerfoundation.org/facts/rare/mc/index.htm