Malignant large bowel neoplasms

Epidemiology:

• Second most common malignancy (behind ca bronchus)
• Peak age incidence is in those > 60yrs

Aetiological factors:

Diet:

• Bile salt conversion: It is believed that a diet rich in animal fat is a major risk factor. Such a diet (common in the Western world) produces an environment within the gut which favours the bacterial conversion of bile salts to carcinogens.
• Low intake of fibre: This slows down gut transit time and, therefore, increases the time of exposure of the mucosa to carcinogens.

Adenomatous polyps:

Genetic factors:

• FAP is an inevitable cause of cancer
• 2-3x increased risk to a first-degree relative of a pt with adenocarcinoma. This hereditary non-polyposis colon cancer (HNPCC) probably accounts for ~10% of colon malignancies.

Inflammatory bowel disease (CD and UC)

Pathological features:

Distribution:

• Rectum 57%
• Sigmoid colon 21%

Synchronous lesions:

• Up to 3% of pts have one or more synchronous cancers
• 75% of pts have a benign adenoma

Macroscopic classification:

• Polypoid
• Ulcerative
• Annular
• Combination of the above

Spread:

• Direct extension
• Lymphatic (largely upwards to the aorta and portal vein)
• Haematogenous (mainly to liver)
• Transcoelomic (can lead to ascites)
• Direct implantation (iatrogenic)

Staging – Dukes classification:

Duke’s A: The tumour is confined to the mucosa. 5yr survival is 90%

Duke’s B: The tumour has extended through all the muscle layers and has possibly reached the serosa. There are NO metastases to lymph nodes. 5yr survival is 60%

Duke’s C: As for stage B but with lymph node metastases.

Duke’s C1 – local lymph node involvement only

Malignant large bowel neoplasms

Duke’s C2 – Distant lymph node involvement

5yr survival is 30%

Duke’s D: This was not part of the original classification. Indicates distant metastases or residual disease following surgery. 5yr survival is 5%

Clinical features:

• Alteration in bowel habit
• Rectal bleeding
• Weight loss
• Abdominal pain
• Malaise
• Tenesmus

Clinical features – right-sided tumours:

• Malaise
• Weight loss
• Vague abdominal pain
• (Occasionally) a self-detected mass in the abdomen

Clinical features – left-sided tumours:

These are much more likely to present with obstructive symptoms

• Colicky abdominal pain
• Change in bowel habit (diarrhoea or constipation)

Clinical features – rectal tumours:

• Rectal bleeding (usually on defaecation)
• Tenesmus

A growth that has spread locally may cause:

• Faecal incontinence from invasion of the anal sphincters
• Back pain because of involvement of the sacral plexus
• UTIs , retrovesical fistula or renal failure through infiltration of the renal tract

Investigation:

PR exam

Sigmoidoscopy:

• Biopsy of any mucosal abnormality

Barium enema (if colonoscopy is unavailable)

Colonoscopy

Assessment of extent of disease and of spread:

• Carcinoembryonic antigen (CEA) is a useful marker of the elimination of disease and the emergence of recurrence
• CT scan

Malignant large bowel neoplasms

Mx – colon carcinoma:

• Duke’s A-C: Surgical excision
• Duke’s B-C: As above + adjuvant therapy
• Right-sided tumours are removed by a right hemi-colectomy
• Left-sided tumours are removed by a resection tailored to the segment of bowel involved.

Mx – rectal carcinoma:

• Mid or upper rectal tumour: Removed by resecting the distal colon and involved rectum and restoring the continuity by joining the large bowel to the stump of the rectum (known as an anterior resection)
• Low rectal tumour: Requires the removal of the whole rectum and adjacent sphincters (abdominoperineal resection and colostomy) and operation usually only carried out by two surgeons – one working within the abdomen and the other from the perineum.

Complications of colectomy and rectal excision:

• Haemorrhage
• Ureteric damage
• Damage to bladder function
• Damage to sexual function
• Damage to duodenum (right hemi-colectomy)
• Damage to spleen (left hemi-colectomy)
• Anastomotic complications (stenosis/leakage)
• Complications of stoma
• Diarrhoea/constipation

Adjuvant therapy:

Radiation:

• Pts with Duke’s B and C rectal carcinoma should receive local deep X-Ray therapy

Chemotherapy:

Although solid-tumours such as colorectal cancers are not very sensitive to chemotherapy, there is evidence that results can be improved in Duke’s B and C by the use of chemotherapy with 5-fluouracil.