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Chapter 4: Gastrointestinal oncology 181

be tubular, villous or tubular-villous dependent on his- Aetiology
tological features. Most colorectal cancers arise from adenomatous polyps
Tubular polyps account for 90% and consist of glan- with a median transition of 20 years. Ulcerative colitis is

dular tubules with a fibrovascular core covered by a associated with an increased incidence.
mucous membrane. Genetic predisposing conditions include familial ade-
Villous adenomas are composed of finger like epithe- nomatous polyposis, hereditary non-polyposis colon

lial projections, spread over a large area within the cancer. There is an overall increased incidence in first-
mucosa. degree relatives.
Tubular villous adenomata are composed of both pat- Dietary factors such as a high animal fat and low fibre

terns. intake.

Clinical features Pathophysiology
Most are asymptomatic but they may cause bleeding and Colonic cancer occurs in the sigmoid colon and rec-
diarrhoea. tum (50%), caecum and ascending colon (30%) and
transverse and descedending colon (20%). Carcinomas
Complications may be polypoidal, ulcerating or stenosing. The tumour
All neoplastic polyps are pre-malignant, low lesions may spreads by direct infiltration into the bowel wall and cir-
prolapse through the anus. cumferential spread. Subsequent invasion of the blood
and lymphatics results in distant metastasis most fre-
Management quently to the liver.
Tubular polyps are resected endoscopically, villous le-
sions require transmural excision or formal resection. Clinical features
Presentation is dependant on the site of the lesion, but in
Prognosis general a combination of altered bowel habit and bleed-
There is a 30–50% risk of recurrence therefore surveil- ing with or without pain is reported. Up to a third of
lance with 3–5 yearly colonoscopy in patients under 75 patients present with obstruction, or perforation. Cae-
years is suggested. cal or ascending colonic cancers often present later with
iron deficiency anaemia. Examination may reveal a mass
(on abdominal palpation or rectal examination), ascites
Large bowel carcinoma
and hepatomegaly.
Definition
Large bowel malignant adenocarcinoma. Macroscopy/microscopy
Raised red lesions with a rolled edge and central ulcera-
Incidence tion.Adenocarcinomasarecomposedofglandulartissue
Lifetime incidence of 1 in 25. Second most common made up of pleomorphic neoplastic epithelial cells.
cause of cancer death.
Investigations
Age Endoscopic examination of the large bowel with
Average 60–65 years. biopsy is diagnostic.
Barium enema or CT pneumocolon may also detect

Sex tumours.
Rectal cancer M > F; colonic cancer F > M. LFTs, liver ultrasound scan and chest X-rays are used
to look for metastatic spread.
Geography Pre-symptomatic disease may be identified by surveil-
Rare in Africa and Asia (thought to be environmental). lance colonoscopy in at risk patients.