Bowel cancer

Question 1

Risk factors

Answer 1

S: Surgery
A: Adenoma in large bowel
F: Family History
E: Environment

IBD and age

Migration to high risk population.
Food rich in meat and fat

Food rich in vegetables and fibre reduce cancer by increase faecal bulk

Question 2

High fibre diet

Answer 2

Increase SCFA = promote healthy gut microbes = induce differentiation, arrest growth of cells and cause apoptosis

Increase stool bulk = reduce e transit time

Reduce secondary BA formation

Question 3

Polyp

Answer 3

Protrusion into hollow viscus

Question 4

Polyp pathological features

Answer 4

Hyperplastic - more goblet cells than normal mucosa
Tubular adenoma - test tube appearance
Villous adenoma - fingerlike
Tubulovillous adenoma

Question 5

Dysplasia

Answer 5

Morphological features of cancer but no invasion

Low grade = early precancerous features

Question 6

Adenoma-carcinoma sequence

Answer 6

Progression of bowel cancer from normal mucosa to adenoma to cancer

Most non-genetic determined = adenoma
Distribution of adenoma = distribution of bowel cancer

Peak incidence predates cancer
Residual adenoma found in early invasive cancer
Number of polyps

Question 7

Familial Adenomatous Polyposis

Answer 7

100 polyps minimum to diagnose
Dysplastic polyps = adenomatic

100% risk of development of cancer by 30yo - prophlylactic colectomy around 20yo

Question 8

FAP genetics

Answer 8

Hereditary autosomal dominant condition
The defective gene is on Chr 5q21 and called APC gene (Adenomatous Polyposis Coli)

Patients acquire the first abnormal gene in utero as germ cell mutation (‘first hit’)
To develop polyps they acquire the second genetic abnormality in the somatic cells (‘second hit’)

Question 9

Loss of heterozygosity

Answer 9

The loss of the second set of normal genetic material during the ‘second hit’ is termed loss of heterozyosity and cells will acquire two identical copies of abnormal genes i.e. become homozygous for the cancer gene
After the second hit the cells acquire more genetic abnormalities to progress with adenoma-carcinoma sequence

Question 10

Hereditary non-Polyposis Colorectal Cancer (HNPCC)/Lynch Syndrome

Answer 10

Affecting predominantly the caecum and right colon, before the age of 50

Question 11

Genetics of HNPCC

Answer 11

Mismatch of base pairs during replicating
G-C -> G-T (no repair genes)
Errors accumulate
Errors in repeat nucleotide

MSH2 (2p16), MLH1 (3p21), PMS 1 and 2

Question 12

HNPCC Amsterdam Criteria

Answer 12

3+ relatives 
One should be first degree of other 2 
2 or more generations (successive) 
Before 50yo
FAP excluded

Question 13

Diagnose bowel cancer

Answer 13

History and clinical exam
Anaemia
Flexible sigmoidoscopy and colonoscopy

Question 14

Bowel cancer symptoms

Answer 14

Change in bowel habit, constipation etc
Bleeding form rectum
Anaemia
Abdominal pain

Question 15

Duke’s staging

Answer 15

x

Question 16

TNM staging

Answer 16

T1 – cancer involves the submucosa
T2 – cancer involves inner of muscularis propria
T3 – cancer involves full thickness of the bowel wall i.e. inner and outer layers of muscularis propria
T4 – perforated cancer or cancer cells on serosal surface
N1 – less than four LN with metastasis
N2 – four or more LN metastasis
M1 – distal metastasis (liver)

Question 17

Stool Testing

Faecal Occult Blood Testing (FOBT)

Answer 17

Testing for occult i.e. hidden blood in the stool, not visible to the naked eye
Men and women 60 – 69yrs initially ( extended to 75 yrs in 2007 ) are invited to participate
Test performed every two years
Positive test does not mean one has bowel cancer
Haemorrhoids & inflammation can cause a positive test

Question 18

Stool test

Answer 18

Ulcerating cancer bleeds silently
Trauma to large polyps due to friction with stool also causes bleeding
The blood in the stool reacts with a chemical to show there has been bleeding and the sample turns blue