Fact-sheet: Colorectal carcinoma


Updated on 09/24/2025 at 12:50 AM

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Definition

Colorectal cancer is a malignant tumor arising from the epithelial cells of the colonic or rectal mucosa.

Adenocarcinoma is the most common histologic subtype.

Colon cancer is a major public health issue, with particular emphasis placed on screening.

Clinical features

Symptoms of colorectal cancer are often nonspecific and may include:

  • Recent changes in bowel habits (constipation, alternating diarrhea and constipation)
  • Rectal bleeding
  • Abdominal pain
  • General deterioration in health status
  • Unexplained iron-deficiency anemia
  • Palpable abdominal mass

Laboratory findings

Carcinoembryonic antigen (CEA) level: Used for follow-up

Radiography

Abdominal radiograph. Nonspecific and insensitive. Obsolete.

  • Air-fluid levels in cases of obstruction, but cannot distinguish mechanical obstruction from paralytic ileus.
  • Cecal distension, whose diameter should be monitored given the risk of diastatic perforation beyond 10 cm.
  • "Coffee bean" sign suggestive of sigmoid volvulus.

Ultrasound

Ultrasound may show:

  • Hypoechoic bowel wall thickening.
  • "Pseudokidney" sign due to luminal narrowing.
  • Loss of wall layer differentiation.
  • Presence of small lymph nodes (< 7 mm).
  • Anechoic tubular structures in cases of colonic varices.
  • Liver metastases, most often hypoechoic, showing portal and delayed phase wash-out on CEUS.

CT

Reference examination

Positive diagnosis:

  • Focal wall thickening or polypoid lesion.
  • Asymmetric thickening with heterogeneous enhancement after contrast administration.
  • Narrowing or stricture of the colonic lumen.
  • Infiltration of the adjacent fat.
  • Satellite lymph nodes.

Staging workup:

  • Local extension: size, relationships with adjacent structures.
  • Regional extension: mesenteric lymphadenopathy.
  • Distant extension: hepatic, pulmonary, and peritoneal metastases.

Assessment for complications:

  • Obstruction: upstream colonic dilation, air-fluid levels.
  • Perforation: pneumoperitoneum, bowel wall pneumatosis.

Differential diagnosis:

  • Diverticulitis.
  • Other colonic tumors.

CT-specific techniques:

  • Water-enema CT colonography: Improves detection of wall thickening and allows better assessment of the colonic lumen.
  • Virtual colonoscopy: A less invasive technique than optical colonoscopy, allowing visualization of polyps and cancers

MRI

Very useful +++ for locoregional staging of rectal cancer.

Imaging protocol:

  • T2-weighted sequences without fat suppression for excellent contrast between the different structures.
  • Sagittal, axial, and coronal slices for multiplanar analysis.
  • Axial T1
  • Axial Diffusion
  • Marking with ultrasound gel and glucagon
  • Gadolinium injection (optional).

Advantages of MRI:

  • Better assessment of the circumferential margin compared to endorectal ultrasound.
  • Better analysis of distant organs.

MRI allows:

  • Determination of the T stage based on tumor infiltration.
  • Assessment of the circumferential resection margin.
  • Analysis of lymph nodes.
  • Detection of sphincter involvement in low rectal cancers.

Vascular intervention

Stent placement to restore digestive continuity in cases of obstructive rectal cancer, either as a palliative measure or prior to surgery.

Nuclear medicine

99mTc-labeled red blood cell scintigraphy: Allows localization of active lower gastrointestinal bleeding.

111In-labeled octreotide scintigraphy: Useful for staging colonic carcinoid tumors.

18FDG PET: Allows regional and distant staging of colonic cancers, as well as localization of tumor recurrences.

Management

Optical colonoscopy: Reference examination for diagnosis and biopsy.

Imaging: Crucial role at all stages of diagnosis and follow-up.

Multidisciplinary management: Surgery, chemotherapy, radiotherapy.

Classification

TNM Primary tumor (T)

  • Tis: Intraepithelial tumor (carcinoma in situ) or invasion of the lamina propria
  • T1: Tumor invading the submucosa without extending beyond it,
  • T2: Tumor invading the muscularis propria without extending beyond it,
  • T3: Tumor invading the subserosa and/or non-peritonealized pericolic tissue,
  • T4: Tumor invading at least one adjacent organ and/or the visceral peritoneum T4a: Invasion of the visceral peritoneum
  • T4b: Invasion of an adjacent structure
  • Tx: the primary tumor cannot be assessed.

TNM Regional lymph nodes (N)

  • N0: no lymph node metastasis
  • Nx: lymph nodes not assessed
  • N1: 1 to 3 metastatic regional lymph nodes N1a: 1 lymph node
  • N1b: 2-3 lymph nodes
  • N1c: tumor deposits in the subserosa or non-peritonealized pericolic or perirectal tissue, without metastatic lymph nodes
  • N2: 4 or more metastatic regional lymph nodes N2a: 4-6 lymph nodes
  • N2b: 7 or more lymph nodes

TNM Metastases (M)

  • M0: no metastasis
  • M1a: Distant metastases confined to one organ without peritoneal involvement: liver, lung, ovary, non-regional lymph nodes
  • M1b: Metastases involving more than one metastatic site
  • M1c: Peritoneal metastasis with or without other organ involvement

Endorectal ultrasound classification of anal cancer:

  • T1: Involvement of the mucosa and submucosa without involvement of the internal sphincter
  • T2: Involvement of the internal sphincter without involvement of the external sphincter
  • T3: Involvement of the external sphincter
  • T4: Involvement of an adjacent pelvic organ

Differential diagnosis

Benign tumors: Polyps, lipomas, villous tumors.

Malignant tumors: Lymphomas, stromal tumors, carcinoid tumors.

Inflammatory or infectious conditions: Diverticulitis, Crohn disease, ulcerative colitis.