This graphic from the most recent 7th edition AJCC
(American Joint Committee on Cancer) might clear some things up in this conversation. It also compares the TNM staging directly to other methods. FWIW, there is no comparable Dukes staging classification for TNM Stages IVa or IVb.
If you were dx'd with "Stage IV colon cancer that apparently started in my upper rectum region, spread thru the wall, entered 1/9 lymph nodes that we know of and went ahead and attached itself to my uterus, cervix and top of my vagina", then you are:
- ANY T
- ANY N
- M1b (Metastases in more than one organ/site or the peritoneum)
For a T4b, "Tumor directly invades or is adherent to other organs or structures." Everything counts as another "organ or structure."
Cancer adherent to or present in the uterus, cervix and vagina is considered "more than one organ or site." And as someone else mentioned, "distant" is a relative term. They are all adjacent to the colon, but they are considered multiple "distant" sites.
Your clinical staging (scans, etc.) if it confirmed tumor attachment to uterus, cervix and vagina, would put you at Stage IVb. It's not up to "the doctor" and s/he has no discretion in staging if s/he's working according to the AJCC guidelines.
And yeah - accurate evaluation of your staging makes a difference. For one thing, it determines which drugs you're eligible for as first and second line treatments, and what kind of medical follow-ups your insurance company will authorize.