How rare is this

Rarity?

Welcome to the boards, though it is not a place anyone wants to be and not something we like to see as another sets forth on this journey.  That being said it is a very good place to be for questions, answers, jokes, venting and everything else.  I have found a lot of help and support here since I joined (my trip started basically in January).  It has helped getting through my surgery and the aftermath.  In fact I am sitting with my pump attached from yesterday, my 6th chemo session.  Though not easy, it is totally doable.  In fact in the last week I went to 5 baseball games near me (minor league team) and had an absolute blast.  And at not point did I think about the cancer or chemo, though yesterday I went with a bit of extra clothes to cover the pump

As to staging, this set forth the general guidelines.

http://www.cancer.org/cancer/colonandrectumcancer/detailedguide/colorectal-cancer-staged

That being said, they change that from time-to-time and the stats for survival change often.  Treatments change and the stats are rolling a bit bit, meaning that most recent updates may not relfect recent advances as they stand today, plus there is also variations from person based on various factors, including general health.

I was staged as IIIC and there are suspect areas in other parts.  I had a PET scan and also have another scan waiting in about 6 weeks.  Being monitored on areas in lungs, liver and kidneys which may or may not be something.  There seem to be things which did not appear on other tests I have had in recent years, for things unrelated to cancer, so they may not be as accurate or looking quite the same based on what they (old tests) were looking for.  

Your doctor could confirm the staging, though based on the mets it sounds like Stage IV.  Once again, check with your Doc.   I asked the same question of my Onc.  He basically said, Stage IIIC or Stage IV would not change the immediate game plan for me, that if something is there, they will go in and take it out.  (I had a fairly large tumor in the asecending colon, had about 1/3 of my colon removed, and it was in over half of the immediate lymph nodes in the area, I had 20 removed, it also moved into tissue, but my surgical margins were all clean).  My case is different than yours in terms of the mets being confirmed or not.  Not sure what the implication is in terms of rarity for you with the mets into lungs and neck, but try not to get too hung up with the worry and do what you need to do.  

I have two friends who are recently 5 years NED (different cancer types than colon, but both Stage IV and "worse" than mine.)  My one friend, when I started talking with him and mentioned the staging for me, said basically "Screw that, do what you got to do and do not worry too much about staging."  Not that it is not part of this all, but more to avoid the fear or anxiety that may come with the numbers.  Sometimes easier said than done, and I am sure I will be like a cat on a hot tin roof as the next scan draws closer, but I am avoiding dwelling on the bad and focusing on the good.  There are times where it does hit me a bit, but it goes by.  Actually the last day I was sort of anxious or whatever word is proper pending the 6th treatment which is longer than I normally have had since this started.  Almost a day where it was grinding me (usually it is 5-10 minutes or less where I think "ah s--t"), but going to the game last night knocked that all away instantly, and I back to looking forward to each day and getting done with this.

Hang in there, and welcome once again.