COLON CANCER Flashcards
What is the most common type of polyp found in the GI tract? Where is it typically found? What does it look like on biopsy?
- Hyperplastic polyp
- Rectosigmoid colon
- sawtooth or serrated pattern
In contrast to hyperplastic polyps, which polyps found in the GI tract are dysplastic and have malignant potential?
how can these polyps be subclassified?
Adenomatous polyps
Can be subclassified by: shape (sessile, pedunculated); histology (tubular, villous)
What is the most common histological type of adenomatous polyp?
which histological type is more likely to develop into colon cancer?
80% are tubular
20% are villous: often sessile, long projections extending from surface. High risk of development into colon cancer (= VILLAIN)
What is a juvenile polyp?
Where is it normally found?
What symptoms does it normally produce?
Benign tumour (hamartoma) that occurs in children - usually in rectum
- Often pedunculated
- Cause painless rectal bleeding and can auto-amputate
What might a child have if they have more than 10 juvenile polyps? What investigation is important for these children and why?
Juvenile polyposis syndrome
Increased risk of cancer: surveillance colonoscopy required
Which GI condition should you consider a child presenting with the following symptom?
what is an important risk associated with this condition?
Peutz-Jegher syndrome
Autosomal dominant disorder characterised by multiple hamartomas throughout GI tract
Risk of gastric, small intestine and colon cancer
What are the two well-defined genetic pathways associated with colon cancer?
- Chromosomal instability (adenoma-carcinoma sequence)
- Microsatellite instability
Tumours in occurring via chromosomal instability pathway are most likely to be found where in the GIT?
what is the 3 steps of the chromosomal instability pathway?
Left-sided colon
Step 1: mutation of APC gene: tumour suppressor gene → at risk colon
Step 2: mutation of KRAS gene: proto-oncogene → adenomatous polyp formation
Step 3: mutation of P53_ gene_: tumour suppressor gene → colon cancer
Which autosomal dominant disorder is caused by a germline mutation of the APC gene? What does this lead to? What is the treatment?
Familial adenomatous polyposis (FAP)
- Always progresses to colon cancer
- Treatment with colectomy
Somebody with an APC mutation and the following presentation is likely to have which condition?
Gardener’s syndrome
form of familial adenomatous polyposis (FAP) characterised by multiple colorectal polyps and various types of tumors
Tumours developing via the microsatellite instability pathway are more likely to be found in which part of the GI tract?
Right-sided colon
Mutations in which genes are responsible for microsatellite instability?
Mismatch repair genes: increases risk of mismatches in DNA microsatellites
Which hereditary condition is associated with an inherited mutation of DNA mismatch repair enzymes?
Lynch syndrome (hereditary non-polyposis colorectal cancer)
- tumours arise de-novo, without pre-existing adenoma
- endometrial cancer common; also ovarian, stomach
- classically causes right sided colorectal cancer
Why is aspirin thought to reduce risk of colorectal cancer?
Thought to reduce risk by 20 to 40%
There is an increased expression of cyclo-oxygenase 2 in colon cancer cells
Where would you expect the GI tract tumour to be in someone presenting with an iron deficiency anaemia and weight loss? By which pathway would you typically expect this tumour to have formed?
Right-sided (proximal/ascending)
Microsatellite instability pathway e.g. Lynch syndrome
Where would you expect the tumour to be in a patient presenting with blood streaked stools which they describe as pencil thin? Which pathway would you expect this tumour to have been formed by?
Left-sided colon due to circumferential lesions which cause a change in stool calibre
Adenoma carcinoma sequence i.e. chromosomal instability pathway
What is the most common site of metastases from colon cancer?
Liver
Where is Streptococcus gallolyticus (formally Bovis) normally found in the body? If it causes an endocarditis or bacteraemia what is the next investigation you should carry out? Explain why
Normal colonic bacteria
Strongly associated with colon cancer when it causes bacteraemia all endocarditis
Streptococcus gallolyticus (formerly known as S. bovistype I) is main causative agent of septicemia and endocarditis in elderly and immunocompromised. It belongs to the few opportunistic bacteria, which have been strongly associated to colorectal cancer.
