Carcinoma of the colon, rectum and anus

Question 1

Carcinoma of the large bowel. Go into more depth about the genetic factors? What genes ect.?

Answer 1

Genetic aetiology:

• Familial adenomatous polyposis (FAP) is responsible for <1% of cancers, and occurs due to tumour suppressor gene APC mutations
• Hereditary non-polyposis colorectal cancer (HNPCC) is responsible for <5% of all cancers, and arises from germline mutations in mismatch repair genes
• Most cancer are sporadic however, occurring without family history

Question 2

Describe the morphology/natural history of carcinomas of the large bowel

Answer 2

• Adenocarcinoma, with characteristic ‘singlet ring cells’ on histology.
• The vast majority of colorectal cancers occur in the recto-sigmoid region
  
  • Caecum & Ascending colon: 15%
  • Transverse colon: 10%
  • Descending colon: 5%
  • Sigmoid colon: 25%
  • Rectum: 45%
• They usually appear as a polypoid mass with ulceration, spreading initially by direct inflitration through the bowel wall.
• It then involves the lymphatics and blood vessels, metastasising primarily to the liver. Transcoelomic spread can also occur

Question 3

What are the main two types of carcinomas of the large bowel?

Answer 3

Many carcinomas develop sporadically, and originate from benign adenomas (polyps). Tubular adenomas (90%) start off as smaller swellings but develop into pedunculated structures, with hyperchromatic dysplastic glands. Villous adenomas (1%) most commonly occur in the rectum. They form a smaller mass which may be quite large and have a delicate frond-like structure, with a broad base and no pedicle. The fronds are formed of dysplastic epithelium.

Question 4

What are the risk factors and protective factors for carcinoma of the large bowel.

Answer 4

Risk factors:

• Family history
• age
• western diet (low in fibre, high in fats)
• ulcerative colitis
• smoking

Protective factors:

• Fruit & vegetables
• exercise
• hormone replacement therapy
• aspirin/NSAIDs

Question 5

What are the common symptoms/signs suggestive of carcinoma of the colon, rectum and anus?

Answer 5

Any colorectal tumour may present with an abdominal mass, abdominal pain, haemorrhage, perforation or fistula

• Right sided (proximal) tumours are more often asymptomatic, and may present with iron deficency anaemia/weight loss
• Left-sided tumours more commonly present with PR (rectal) blood/mucus, altered bowel habit, tenesmus (crampling rectal pain), obstruction and a mass on PR examination
• Anal tumours may be present with bleeding, pain, changes in bowel habit, pruritis ani, masses or a stricture

Question 6

What is the staging system used for colorectal cancers?

Answer 6

Duke’s Staging:

• Duke’s A: Tumours invade submucosa +/- muscularis propria
• Duke’s B: Tumours invade past the muscularis propria (into subserosa/directly into other organs, but no nodal involvement)
• Duke’s C: Regional lymph node involvement
• Duke’s D: Distant metastases