Colorectal cancer

Last revised by Dr MT. Niknejad on 06 Sep 2022

Colorectal cancer is the most common cancer of the gastrointestinal tract and the second most frequently diagnosed malignancy in adults. CT and MRI are the modalities most frequently used for staging. Surgical resection may be curative although five-year survival rate is 40-50%. 

Colorectal cancer is common, accounting for 15% of all newly diagnosed cancers, and tends to be a disease of the elderly, with the median age of diagnosis between 60 and 80 years of age 2, slightly younger for rectal cancer. There is also a slight male predilection for rectal cancers, not found in tumors elsewhere in the colon. 

A number of predisposing factors have been identified, including:

Recognized hereditary syndromes are seen in 6% of colorectal cancers. These include:

Clinical presentation is typically insidious:

However initial manifestation may be acute:

Less common presentations include:

  • that of metastatic disease (e.g. respiratory symptoms from lung metastases)
  • paraneoplastic syndromes (e.g. dermatomyositis)
  • bacteremia or bacterial endocarditis with Streptococcus bovis (Streptococcus gallolyticus6

In general:

  • right-sided tumors are larger and present with a mass, distant disease or iron deficiency anemia
  • left-sided tumors present earlier with altered bowel habit

Colorectal cancers, 98% of which are adenocarcinomas, arise in the vast majority of cases from pre-existing colonic adenomas (neoplastic polyps), which progressively undergo a malignant transformation as they accumulate additional mutations 2 (so-called multi-hit hypothesis). 

Morphologically cancers can be:

  • sessile
  • exophytic
  • circumferential (apple core
  • ulcerated 
  • desmoplastic

Rarely the malignant cells will widely invade the submucosa, analogous to linitis plastica of the stomach. These are typically scirrhous adenocarcinomas (signet-ring type).

Metastases may be widespread in advanced disease, although the liver is by far the most common site involved.

Colorectal cancers can be found anywhere from the cecum to the rectum, in the following distribution 2,5:

  • rectosigmoid: 55%
  • cecum and ascending colon: ~20%
    • ileocecal valve: 2%
  • transverse colon: ~10%
  • descending colon: ~5%

Approximately 10% of colorectal cancers have a BRAF mutation, which is more common in females, right colon colorectal cancer, advanced stage at diagnosis, and a mucinous histology 7

See: colon cancer staging.

  • sensitivities for polyps >1 cm
  • polyps <1 cm: <50% detection 3

Appearances will reflect macroscopic appearance, with lesions seen as filling defects. These need to be differentiated from residual fecal matter. Typically they appear as exophytic or sessile masses or maybe circumferential (apple core sign). Fistulas to bladder, vagina, or bowel may also be demonstrated.

Rarely the stenotic segment will be long particularly with scirrhous adenocarcinomas.

CT is the modality most used for staging colorectal cancer, with an accuracy of only between 45-77% 4, able to assess nodes and metastases.

It is often able to diagnose tumors although it is insensitive to small masses. CT colonography is increasing in popularity as an alternative to colonoscopy.

Most colorectal cancers are of soft tissue density that narrow the bowel lumen 4. Ulceration in larger masses is also seen. Occasionally low-density masses with low-density lymph nodes are seen in mucinous adenocarcinoma, due to the majority of the tumor composed of extracellular mucin. Psammomatous calcifications in mucinous adenocarcinoma can also be present.

Complications may also be evident, e.g. fistulae, obstruction, intussusception, perforation 4.

MRI has a staging accuracy of 73% with a 40% sensitivity for lymph node metastases 1. MRI is having an increasing role to play in the staging of rectal cancer.

Treatment involves local control with resection in almost all cases. Adjuvant chemotherapy is reserved for stage III disease.

Overall 5-year survival rate is 40-50%, with the stage at operation the single most important factor affecting prognosis.

  • Dukes A: 80-90%
  • Dukes B: 70%
  • Dukes C: 33%
  • Dukes D: 5%

BRAF-mutated colorectal cancer has a poorer prognosis with a median survival of <12 months 7.

Recurrence is common:

The tumor marker carcinoembryonic antigen (CEA) is routinely used for detecting postoperative early recurrence and metastatic disease (especially liver disease). It is also used for monitoring response to treatment of metastatic disease.

  • as with most tumor markers, it is inappropriate for screening given its poor sensitivity and specificity
  • higher levels of CEA are associated with:
    • higher grade tumors
    • higher stage disease
    • visceral metastases (especially liver metastases)

Screening recommendations are contentious and vary widely from country to country. An example would be:

  • for persons >50 years of age: an annual fecal occult blood test (often a fecal immunochemical test (FIT)) and sigmoidoscopy/barium enema every 3 to 5 years
  • for first-degree relatives of patients with colon cancer: screening should start at age 40

On CT colonography, the two most useful discriminators of colorectal carcinoma and diverticular disease are absence of diverticula within the structured segment, and shouldered edges, with both features having a high negative and positive predictive value for carcinoma 8. Other features pointing to carcinoma include a shorter segment length, destroyed mucosal folds, straightening of the segment, absence of thickened fascia, and more and larger locoregional nodes.

Other imaging differential considerations on CT include:

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Cases and figures

  • Figure 1: gross pathology - stenosing adenocarcinoma
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  • Figure 2: gross pathology - with extramural spread
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  • Figure 3: CT/MRI/gross pathology
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  • Case 1: with colovesical fistula
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  • Case 2: barium, sigmoid
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  • Case 3: MRI, rectosigmoid
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  • Case 4: hepatic flexure
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  • Case 5: cecal causing small bowel obstruction
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  • Case 6: descending colon
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  • Case 7: with background FAP
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  • Case 8: apple core sign
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  • Case 9: rectal, with ulcerative colitis
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  • Case 10: cecal adenocarcinoma
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  • Case 11: rectosigmoid with hepatic deposit
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  • Case 12: sigmoid with large bowel obstruction
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  • Case 13: descending colon
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  • Case 14: rectosigmoid, perforated
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  • Case 15: sigmoid, with metastases
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  • Case 16: cecal on barium study
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  • Case 17: descending colon
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  • Case 18: ascending
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  • Case 19: ascending
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  • Case 20: cecal
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  • Case 21: splenic flexure
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  • Case 22: rectosigmoid
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  • Case 23: sigmoid T4a N2
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  • Case 24: within a sigmoid diverticular segment
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  • Case 25: cecal with appendiceal mucocele
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  • Case 26: descending
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  • Case 27: rectosigmoid with peritoneal carcinomatosis
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  • Case 28: causing intussusception
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  • Case 29: rectosigmoid, with rectal contrast
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  • Case 30: ascending
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  • Case 31: metastatic rectosigmoid
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  • Case 32: descending
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  • Case 33: locally advanced cecal
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  • Case 34: cecal and ascending
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  • Case 35: hepatic flexure, barium enema
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  • Case 36: ascending colon adenocarcinoma
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  • Case 37
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  • Case 38: ileocecal adenocarcinoma
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  • Case 39: sigmoid colon adenocarcinoma
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  • Case 40: metastatic
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  • Case 41: causing ileocolocolic intussusception
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  • 42: metastatic
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  • 43: ileocecal adenocarcinoma
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  • Case 44: Transverse colon cancer
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  • Case 45: causing colocolic intussusception
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  • Case 46: metastatic
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  • Case 47: causing intussusception
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  • Case 48: metastatic sigmoid colon cancer
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  • Case 49
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  • Case 50: metastatic and obstructing
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  • Case 51
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  • Case 52
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