Diagnostics of cancer in the colon and rectum
The purpose of the diagnostic tests is to assess whether cancer is present and to identify the stage of the disease.
The clinical examination should include a thorough history of the disease and abdominal and rectal palpation. Recently appearing symptoms must be examined without delay. A considerable “doctor’s delay” may be due to the lack of these clinical examinations.
- CEA (carsino-embryonal antigen) is used to identify advanced stage (CEA above 50 strongly indicates metastatic stage). It is also used to monitor recurrence after supposed curative operation. CEA is only elevated in 50% of the patients with cancer in the colon-rectum, and can therefore not be used as a screening test.
- Examinations for occult blood in the feces are applied for alarming symptoms without simultaneous macroscopic blood in feces. There are two main kinds of such tests. One is based on guiac testing (FOBT), the other is an immunologic test (FIT). Both tests are fairly sensitive, but not very specific.
- Liver test are performed for identified liver metastases
Proctoscopy with biopsy
When there is a suspicion of cancer located in the lower part of the gut the rectum should always be examined, either with a rigid sigmoidoscope or a flexible colonoscope. With the rigid sigmoidoscpope an experienced examiner can visualize the lower 20-25 cm of the gut. Small lesions located in the lower part, especially dorsally, may easily be missed by examination can be rather painful when a cancer is present and a flexible scope may be more lenient and provide a more thorough examination.
Rigid sigmoidoscopy should always be performed as this will more accurately identify the level of the tumor from the anal verge.
Flexible endoscopy is the primary choice when cancer of the colon is suspected. All patients with a cancer should have a total colonoscopy preoperatively to identify synchronous polyps or cancers. If the tumor lumen cannot be penetrated a total colonoscopy should be performed within 3 months postoperatively. Preoperative CT-colography can be performed in such cases.
All tumors are biopsied during endoscopy. Not infrequently forceps-biopsy will underestimate the stage. Polyps with low grade dysplasia may in about 30% contain high grade dysplasia. In case of cancer the biopsy will show only dysplasia in up to 40% of cases. The macroscopic appearance is therefore important. In case of definite cancer by endoscopy, a benign biopsy cannot be considered of definite importance and re-biopsy should be performed.
CT colegraphy/ Virtual coloscopy
The examination is performed with CT double contrast and provides a 2- or 3-dimensional image of the bowel lumen. Polyps and tumors above 1 cm are nearly always identified.
Examinations for loco-regional staging
For a trained endoscopist the macroscopic appearance will give a good indication whether a T1, T2, or a T3 cancer is present, still additional imaging is important.
CT of the abdomen is applied for the staging of cancer of the colon. It acceptably differentiates between T1-2 and T3 cancers (whether there is penetration of the bowel wall.). It can also identify infiltration into neighbouring organs, and whether there are enlarged (or irregular) lymph nodes as sign of stage III disease.The specificity for lymph node metastases is unfortunately low. Additionally the anatomy of the mesocolic vessels can be described which may be of help to the surgeon.
MRI rectum/ pelvis
MRI of the rectum/ pelvis is the examination of choice for T3 and T4 cancer in the rectum. The examination is less accurate regarding T1 and T2 cancers which are often overstaged. Similarly ,benign broad based polyps will often be staged as infiltrating cancer (most often considered mrT2). MRI as the sole indication of cancer should therefore never be trusted. MRI is also the best examination for lymph node metastases in the mesorectum, along the pelvic wall and the inguinal region. The specificity is not very high and only lymph nodes which an experienced MRI radiologist consider definite metastases should be taken into account. MRI is also the method of choice for the estimation of the distance from tumor or mesorectal lymph node metastases to the mesorectal fascie. A distance of 2mm or less is indication for neoadjuvant treatment in patient who can tolerate such treatment. In locally advanced cancer the MRI can identify to the surgeon if and how an extended TME can be performed. The MRI examination must be performed in a standardized way and it requires great dedication and skill to interpret the images.
This is the best examination for rectal cancer at an early stage (T1-TY2) and should be mandatory before local excision of rectal cancer. It is the technique of choice for the sm- staging. It is also possibly the best technique for identifying infiltration into the prostate. Unfortunately few doctors in Norway are skilled in this technique.
Examinations for evaluation of distant spread.
- CT of the lungs is mandatory for the evaluation of lung metastases. Uncharacteristic lesions of up to 6 mm should not be considered during evaluation of primary treatment.
- CT of the abdomen is always performed to identify liver metastases or peritoneal carsinomatosis. In some rare cases lymph node metastases central to the regional area, metastases in adrenal glands or other areas may be identified.
- MRI of the liver is applied to verify suspected metastases. Performed according to a specific protocol this is more sensitive and specific than CT of the liver.
- Contrast enhanced ultrasound (CEUS) of the liver is sometimes performed to differentiate between small cysts and metastases.
- PET-CT is seldom indicated at the time of diagnosis. It can give additional information on distant metastases in rare localisations. PET-CT is not considered better than CT for evaluation of lung/ liver spreading, but may be appropriate in cases of recurrence after previous treatment.