cancer 13 Flashcards
what does the colon do?
- Extraction of water from faeces
- Faecal reservoir
- Bacterial digestion for vitamins
describe the anatomy of the colon?
- The mucosa is folded but it is smooth
- There is a thick muscle layer (muscular)
- the cells of the colon are divided into crypts where the stem cells are found , they are then shunted up to the top of the villus where they are shed

what kind of cancers are colon cancers?
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what is the rate of turnover of cells in the colon?
- 2-5m cells per minute die in the colon -> high proliferation rate
what does APC normally do?
what does the APC mutation do to the cells?
- the gene product of APC reduces the risk of mistakes during replication
- APC mutation prevents cell loss and causes cell proliferation
what are the normal protective mechanisms of the cells of the gut?
- natural loss
- DNA monitors
- repair enzymes.
what is a polyp?
- any projection from a mucosal surface into a hollow viscus, and maybe hyperplastic, neoplastic, inflammatory, hamartomatous.
what are the types of colonic polyps?
-they can be :
- Metaplastic/hyperplastic
- Adenomas - Juvenile, Peutz Jeghers, lipomas (less common)
define adenoma:
benign neoplasm of the mucosa.
what are hyperplastic polyps?
how common are they?
how many have mutations?
- very common growths
- Constitute 90% of all colon polyps
- there are often multiple
- they have no malignant potential
- 15% has a K- Ras mutation
what are colonic adenoma types?
- Tubular = 90% (most common) (>75% tubular)
- Tubulovillous = 10% (less common) (25=50% villous)
- mix between tubular and villous
- Villous ( >50% villous)
- the more villous, the worse it is
what is the anatomy of the adenoma?
- Pedunculated adenomas are on a stalk they look a bit like a tree
- Sessile adenomas are flat and raised
- these can be tubular, tubulovillous or villous

what is the microstructure of tubular adenomas?
- Columnar cells with nuclear enlargement, elongation and multi-layering and loss of polarity. - Proliferation. - Reduced differentiation. - Complexity/disorganisation of architecture.
what is the microstructure of villous adenomas?
- Mucinous cells with nuclear enlargement, elongation, multi-layering, and loss of polarity
-
Exophytic -frond-like extension
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what is dysplasia?
abnormal growth of cells with same features of cancer - categorised into indefinite, low grade and high grade
what is FAP?
- this stands for Familial Adenomatous Polyposis
- it is a 5q21 gene mutation
- the site of mutation determines clinical variants
- i.e. classic, attenuated, Gardner, Turcot
- patients with FAP develop thousands and thousands of polyps
what do patients with FAP undergo?
- prophylactic colectomy
how many adults have adenomas at 50?
how many of these adenomas might become cancerous?
- 25% of adults have adenomas at age 50
- 5% become cancers if left
- the adenomas precede carcinomas by 15 years
- Cancers stay at a curable stage for about 2 years.
do larger or smaller polyps have a greater chance of becoming Colonic Adenomas?
larger polyps
what are the genetic pathways in colorectal cancer?
- Adenoma Carcinoma Sequence
- Microsatellite Instability
- Genetic predisposition for colorectal cancer
explain the adenoma-carcinoma sequence?
- if the gene APC is damaged it can lead to colorectal cancer
- what are microsites?
- what is microsatellite instability?
- Microsatellites are repeat sequences that are prone to misalignment
- some microsatellites are in coding sequences of genes which inhibit growth or apoptosis
what is mismatch repair genes?
what is HNPCC?
- Mis match repair genes recessive genes requiring two hits = without this, there is a very elevated risk of cancer
- HNPCC is when there is a
what are the main genetic pathways leading to colorectal cancer?
- FAP – inactivation of APC TSG.
HNPCC – microsatellite instability
