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Case 8.2 – Colorectal Polyps & Cancer

Category: Surgery | Discipline: Surgery - GIT | Setting: General Practice

Case

Martin Angus, aged 56 years, presents following an episode of rectal bleeding. He feels bad because he has a family history of rectal cancer but was too busy to follow-up on his free colon cancer screen when he received a letter from the Government to have screening done. Now he is really worried he has cancer.

Questions

1. What further history and examination would you undertake?

History:

  • Complete GIT history with particular attention to systemic symptoms (unexplained weight loss, night sweats, change in bowel habits) and more specific details of the bleeding
  • More family history details regarding colon cancer
  • Colonoscopy history - previous results and reason for investigation

Examination:

  • Thorough GIT examination including:
    • Digital rectal examination (PR)
    • Inguinal/femoral lymph nodes assessment
    • Assessment for hepatomegaly
    • Assessment for ascites
2. What are the risk factors for cancer of the colon and rectum?

Risk Factors for Colorectal Cancer:

  • Adenoma-Carcinoma sequence (Fearon/Vogelstein model)
  • Intraluminal chemical carcinogenesis - unclear whether from direct ingestion and/or biochemical processes of existing substances normally found in the faecal stream
  • Dietary factors:
    • Low fibre diet
    • High fat diet
  • Certain types of polyps:
    • Villous adenomas
    • Tubular adenomas
  • Past history of colon cancer
  • Family history of colon cancer:
    • Familial polyposis syndrome
    • Gardner's syndrome
    • Cancer family syndrome (Lynch syndrome)
  • Smoking
  • Obesity
3. What are the screening recommendations in Australia and what is the letter for "poo testing" that Martin is describing?

National Bowel Cancer Screening Program (NBCSP)

What is a Faecal Occult Blood Test (FOBT)?

A FOBT is a non-invasive test which detects microscopic amounts of blood in the bowel motion. Blood is released into the bowel motion in a number of bowel conditions, including bowel cancers and their precursors (polyps or adenomas).

As blood may only be released into the bowel motions intermittently, samples from at least two separate bowel motions are required to increase the chance of detecting this blood.

Important: FOBTs are not a diagnostic test but are used to identify people who require further investigation.

Types of FOBT Available:

  • Guaiac tests - based on the pseudoperoxidase activity of haem (require dietary restrictions)
  • Immunochemical tests (FIT) - utilise antibodies against human haemoglobin (no dietary restrictions required)

NBCSP Uses Immunochemical FIT Because:

  • Higher sensitivity than guaiac tests - suitable for biennial screening
  • No dietary or medication restrictions required - more acceptable to the public
  • Can be easily used at home
  • Has potential for automated analysis

Accuracy of Immunochemical FITs:

  • Can detect 60-90% of cancers and many advanced adenomas under ideal conditions
  • In population screening programs, a person with a positive FIT has:
    • 30-45% chance of having an adenoma
    • 3-10% chance of colorectal cancer

The Bayer DETECT™ Test Sensitivity:

  • 65.8% to 98.9% for colorectal cancer
  • 27.1% to 75.6% for advanced adenomas
  • 85% to 95.6% for colorectal cancer and advanced adenomas combined
  • Specificity: 87.4% to 97.9% in asymptomatic people

How the Screening Works:

  • Eligible participants sent test kit by mail
  • Samples collected at home from two different bowel motions
  • Samples posted to central laboratory (Dorevitch Pathology)
  • Results sent to participant and GP (if nominated) within 2 weeks
  • 6-8% of tests expected to be positive

Follow-up:

  • Positive result: Contact GP within 2 weeks for referral to colonoscopy
  • Negative result: Repeat screening every 2 years; contact doctor immediately if symptoms develop or significant family history discovered
  • Inconclusive result: Repeat test with replacement kit

Colonoscopy Indication:

A person with a positive FOBT is 12 to 40 times more likely to have colorectal cancer than somebody with a negative test. The probability that a person with a positive FOBT has some type of neoplastic lesion is 35-50%.

It is essential that any positive FOBT (even if just one of the samples is positive) is appropriately investigated. Colonoscopy is preferred as it allows for biopsy and removal of adenomas.

4. How do right colon, left colon and rectal cancers differ in presentation in respect to weight loss, feeling a mass, rectal bleeding, Virchow's node, Blumer's shelf, anaemia and obstruction?

Presentation Differences by Site:

Symptom Right Colon Left Colon Rectum
Weight loss + +/0 0
Palpable mass + 0 0
Rectal bleeding 0 + +
Tympany 0 0 +
Anaemia + 0 0
Obstruction 0 + +

Additional Clinical Signs:

  • Virchow's node - Left supraclavicular fossa lymphadenopathy - indicates gastric cancer (not typically colorectal)
  • Blumer's shelf - Palpable metastatic deposit felt on PR examination in pouch of Douglas or retrovesical space - associated with metastatic disease from pancreas/stomach/lung
5. Using diagrams, summarise the operative resection for colon cancer located at: caecum, superior aspect of ascending colon, transverse colon, superior aspect of descending colon, descending colon, and rectum.

Operative Resections for Colorectal Cancer:

The type of resection depends on the location of the tumor and follows the principle of removing the tumor with adequate margins along with its lymphovascular supply.

Tumor Location Operation Description
Caecum Right hemicolectomy Resection of terminal ileum, caecum, ascending colon and hepatic flexure with ileocolic, right colic, and right branch of middle colic vessels
Superior aspect of ascending colon Right hemicolectomy Extended to include hepatic flexure
Transverse colon Extended right hemicolectomy OR Transverse colectomy Resection of transverse colon with middle colic vessels; may extend to include flexures depending on location
Superior aspect of descending colon Left hemicolectomy Resection of splenic flexure, descending colon with left colic vessels
Descending colon Left hemicolectomy Resection of descending colon and upper sigmoid with left colic and sigmoid vessels
Rectum Anterior resection OR Abdominoperineal resection (APR) Anterior resection for upper/mid rectum with colorectal or coloanal anastomosis. APR for low rectal tumors requiring permanent colostomy

Key Surgical Principles:

  • Adequate proximal and distal margins (typically 5cm, but 2cm may be acceptable for rectal cancer)
  • En bloc resection of regional lymph nodes following arterial supply
  • Complete mesocolic/mesorectal excision
  • Restoration of bowel continuity when possible
6. Summarise the staging system for colorectal cancer.

TNM Staging System for Colorectal Cancer

Primary Tumour (T):

  • TX - Primary tumour cannot be assessed
  • T0 - No evidence of primary tumour
  • Tis - Carcinoma in situ: intraepithelial tumour or invasion of the lamina propria
  • T1 - Tumour invading the submucosa
  • T2 - Tumour invading the muscularis propria
  • T3 - Tumour invading through the muscularis propria into pericolorectal tissues
  • T4 - Tumour directly invading other organs or structures or penetrating the visceral peritoneum

Regional Lymph Nodes (N):

  • NX - Regional lymph nodes cannot be assessed
  • N0 - No regional lymph node metastases
  • N1 - Metastases in 1-3 pericolic or perirectal lymph nodes
  • N2 - Metastases in 4 or more regional nodes

Distant Metastases (M):

  • MX - Presence of distant metastases cannot be assessed
  • M0 - No distant metastases
  • M1 - Distant metastases
    • M1a - Metastasis to one site
    • M1b - Metastases to more than one organ/site or peritoneum

Clinical Significance:

The TNM staging system is essential for:

  • Determining prognosis
  • Planning treatment (surgical vs adjuvant therapy)
  • Standardizing communication between clinicians
  • Research and clinical trial stratification