Mock15 FAP
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Stem
You are discussing the results of a follow-up colonoscopy with a young lady. She's very concerned because her father died of colon cancer at a young age.What can you see in this colonoscopy image?
Multiple polyps that vary in size
What's the most probable diagnosis?
FAP
Where else would you expect to find polyps other than colon and rectum?
In stomach and duodenum
Define FAP? What's the mode of inheritance?
Autosomal dominant condition
There is loss of APC tumour suppressor gene on the long arm of chromosome 5
Leading to development of hundreds of tubular adenomas
With 100% risk of cancer by the age of 40Function of APC tumour suppressor gene?
Encodes a factor that negatively regulates the WNT pathway in colonic epithelium (by promoting the formation of a complex that degrades β-catenin)
Can you name other inherited genetic colon cancer syndromes?
Lynch syndrome (hereditary non-polyposis colorectal cancer, or HNPCC)
Peutz-Jeghers syndrome
Cowden syndromeWhat's the classification of intestinal polyps
Non-neoplasticHamartomas
Metaplastic
Pseudo polyps as in UCNeoplastic
Villous
Tubulovillous
TubularCan you name a syndrome with hamartomatous polyp?
Peutz-Jeghers syndrome (PJS)
Define a hamartoma?
Focal or multi focal malformation composed of haphazard arrangements of differ amount of tissues that are normally present in the organ.
Examples: haemangioma and Peutz-Jeghers syndromeWhat are their complications?
Malignant transformation
Intestinal obstruction
Intussusception
Ulceration & Bleeding
Electrolytes disturbance (hypokalaemia)What are the features increasing the risk of malignant change in a polyp?
Type of adenoma, e.g. villous (40%)
Diameter of adenoma:
<1 cm – 5%
2 cm – 20%
Degree of dysplasiaDescribe the sequence of events in malignant transformation of adenoma?
Stepwise accumulation of mutations of oncogenes and tumour suppressor genes:
Loss of APC (tumour suppressor gene) → hyperplasia
K-RAS (proto-oncogene) mutation → dysplasia
Loss of p53 (tumour suppressor gene) → adenocarcinomaWhat's a proto-oncogene, oncogene and tumour suppressor gene?
Proto-oncogenesNormal cellular genes whose products promote cell proliferation.
Oncogenes
Mutated or overexpressed versions of proto-oncogenes that function autonomously, having lost dependence on normal growth promoting signals.
Tumour suppressor genes
Normal genes whose absence can lead to the development of cancer
They act as gatekeepers: inhibit proliferation or promote the death of cells with damaged DNA
E.g. p53 and APC.What are the functions of KRAS?
The KRAS gene provides instructions for making a protein called K-Ras (which is a GTPase protein). This protein is part of a signalling pathway known as the RAS/MAPK pathway.
The protein relays signal from outside the cell to the cell's nucleus.
These signals instruct the cell to proliferate or differentiate.What is Function of P53?
DNA damage and other stress signals may trigger the increase of p53. It's functions are:
Growth arrest at G1 (which prevents replication of damaged DNA).
DNA repair
Apoptosis (cell death) as a "last resort".What's Gardener syndrome?
It's variant of FAP characterised by:
Mandibular osteoma
Desmoid tumours
Sebaceous cyst
Gastric fundal polypsDo you know other FAP variants?
Turcot syndrome (increased risk of brain tumours, mainly glioblastoma and medulloblastoma)
What are the different treatment modalities you would offer this lady with FAP? When?
Subtotal colectomy with ileorectal anastomosis or ileostomy
Pan proctocolectomy with either end ileostomy or IPAA (ileal pouch-anal anastomosis)When will you offer the patient this option, at which age?
At 25 or even younger
Which life-style modifications would be beneficial in reducing cancer risk in patients with FAP?
High fibre diet
Decrease fat intake
Smoking cessation
Stop alcoholIf she has a 2-year-old child, what would be your advice?
Screening by the age of 12 and prophylactic near total colectomy by the age of 25
How to screen?
Start by the age of 13 to 15 years we do annual sigmoidoscopy until age of 20.
By 20 years start to do annual colonoscopy.What's endometriosis?
Endometriosis is defined by the presence of "ectopic" endometrial tissue at a site outside of the uterus.
Due to hormonal changes associated with epithelial changes.Hyperplastic polyps carry a malignant risk or not?
No
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