Hi Jts,
Welcome. This is a great forum and chock full of information and support. You can quell your SO's fears about the cancer spreading that fast. It's already been there for some time. I was diagnosed Nov. 21st 2012 and the surgery to remove the cancerous nodes was on Feb. 7th 2013.
Hang on...there's a hell of a ride coming. Read as much as you can here, take notes, ask questions and stay away from Dr. Google. Just so you know...Dr. Google is currently being sued for false diagnosis/information and causing undue fear and stress. I heard he is actually a computer algorithm devoid of human emotion and compassion

Treatment is brutal but doable. I'm sure many will chime in with great tips and advice.
Positive thoughts and prayers