Colorectal carcinoma

Colorectal carcinoma (CRC) 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 carcinoma 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 carcinoma. There is also a slight male predilection in rectal cancers, not found for tumours elsewhere in the colon. 

Risk factors

A number of predisposing factors have been identified, including:

Associations
Syndromes

Recognised hereditary syndromes are seen in 6% of colorectal carcinomas. These include:

Clinical presentation is typically insidious, with altered bowel habit or iron deficiency anaemia from chronic occult blood loss. Bowel obstruction, intussusception, heavy bleeding and metastatic disease may also be the initial manifestation. Positive blood cultures or bacterial endocarditis with Streptococcus bovis is strongly suggestive of underlying colorectal cancer 6.

In general, right sided tumours are larger and present with a mass, distant disease or iron deficiency anaemia, whereas left sided tumours 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 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 plastic 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.

Location

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

  • recto-sigmoid: 55%
  • caecum and ascending colon: ~20%
    • ileocaecal valve: 2%
  • transverse colon: ~10%
  • descending colon: ~5%
Staging

See: colon cancer staging.

Barium enema
  • 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 faecal matter. Typically they appear as exophytic or sessile masses, or may be 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

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

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

Most colorectal carcinomas are of soft tissue density that narrow the bowel lumen 4. Ulceration in larger mass is also seen. Occasionally low-density masses with low-density lymph nodes are seen in mucinous adenocarcinoma, due to the majority of the tumour 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. MR 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 stage at operation the single most important factor affecting prognosis.

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

Recurrence in common:

The tumour marker CEA is routinely used for detecting post operative early recurrance and metastatic disease (especially liver disease). It is also used for monitoring reponse to treatment of metastatic disease

  • as with most tumour markers it is inappropriate for screening given it poor sensitivity and specificity
  • higher levels of CEA are associated with:
    • higher grade tumours
    • higher stage disease
    • visceral metastases (especially liver metastases)
Screening recommendations

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

  • for persons >50 years of age: annual faecal occult-blood test and sigmoidoscopy/barium enema every 3 to 5 years
  • for first-degree relatives of patients with colon cancer: screening should start at age 40

General imaging differential considerations on CT include:

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Article information

rID: 1153
Section: Pathology
Synonyms or Alternate Spellings:
  • Colorectal carcinoma (CRC)
  • Colon cancer
  • Colorectal cancer
  • Adenocarcinoma of the colon
  • Colorectal carcinomas
  • Colorectal cancers
  • Carcinoma of colon
  • Carcinoma of the colon
  • Carcinomas of the colon

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Cases and figures

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    Figure 1: gross pathology - stenosing adenocarcinoma
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    Case 1: caecal tumour
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    Right hemicolecto...
    Figure 2: gross pathology - with extramural spread
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    CRC with colovesi...
    Case 2: with colovesical fistula
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    Figure 3: CT/MRI/gross pathology
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    Case 3: with small bowel obstruction
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    mucinous colloid ...
    Case 4: mucinous colloid carcinoma of caecum
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    Case 5: well differentiated adenocarcinoma
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    Case 6: causing an intussusception
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    Images show infla...
    Case 7: caecal cancer
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    Case 8
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    Case 9: hepatic flexure with duodenal invasion
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    Case 10: with ileocoecal intussusception
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    Case 11: splenic flexure with hepatic metastasis
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    Case 12
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    Case 13: synchronous colorectal carcinoma
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    Hepatic flexure m...
    Case 14: with hepatic flexure stricture
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    Case 15
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    Case 16: causing small bowel obstruction
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    Case 17
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    Case 18: caecal tumour with large pelvic lipoma
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    Case 19
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    Case 20: with background FAP
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    Case 21: with an entero-colic fistula
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    Case 22: causing large bowel obstruction
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    Case 23
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    Case 24
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    Case 25: stage IV sigmoid colon adenocarcinoma
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    Case 26: mimic RCC
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    Case 27
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