Colorectal cancer diagnosis

I have been diagnosed with Stage 4 colorectal cancer (has metastasized in my lungs). My current CEA level is at 113 after some initial chemo treatments and radiation (The CEA level came down from a high of 372.5 at the 1st of September.) The tumor (mucinous adenocarcinoma), which is pre-sacral and perirectal, did not originate in my colon or rectum per the doctor who performed my last colonoscopy in July. This procedure, as well as two previous colonoscopies, produced a single benign polyp. The tumor measures 11.4 x 11.3 cm and constricts my rectum and bladder (urethra, esp).

Per CT scan:  "Large (11.4 x 11.3 cm) right perirectal mass seen. On this examination performed with rectal contrast, the intimate association of the mass with the lower rectum is more evident, and suspicion is for a rectal origin tumor. However, the differential diagnosis is rather broad, including: sarcoma, chordoma, and teratoma The patient gives a history of bilateral oophorectomy. Therefore, an ovarian origin is considered unlikely.
There is a prominent mass effect seen upon the rectum. No definite fat plane is seen between this mass and the rectum. The remainder of the visualized portions of the bowel are unremarkable, without definite wall thickening or caliber abnormality. No definitely enlarged lymph nodes are seen.
It is unclear if the biopsied mass connects with the rectum or other pelvis structures, or if it is freestanding."

How can they diagnose colorectal cancer based on the results of my colonoscopy? As they have not determined exactly where my cancer originated, what difference, if any, does this make in testing, treatment, etc. Is it important to determine the exact origination point?  I'd appreciate any comments. Thanks.

[Morecambe]

Hi - I'm wondering whether you might obtain a more "in-depth" answer if you place your posting on the "ask a doctor" (Dr Pho's) G.I. forum

regards
Morecambe

[jrinat]

Yes, thank you, I thought I was posting there originally. When I realized where I'd posted I tried to post in the "Related Expert Forum' but could find no way to post. Is this where you can get an answer from a doctor? Thanks for your help.

[Morecambe]

Yes - click on forums at the top of the page and then on the right hand side ("ask a doctor") scroll down to gastroentorology and click on there and follow the step-by-step instructions to post a question.

regards
Morecambe