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Year 2 - Cancer > cancer 13 > Flashcards

cancer 13 Flashcards

1
Q

what does the colon do?

A
  • Extraction of water from faeces
  • Faecal reservoir
  • Bacterial digestion for vitamins
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2
Q

describe the anatomy of the colon?

A
  • 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
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3
Q

what kind of cancers are colon cancers?

A

xxx

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4
Q

what is the rate of turnover of cells in the colon?

A
  • 2-5m cells per minute die in the colon -> high proliferation rate
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5
Q

what does APC normally do?

what does the APC mutation do to the cells?

A
  • the gene product of APC reduces the risk of mistakes during replication
  • APC mutation prevents cell loss and causes cell proliferation
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6
Q

what are the normal protective mechanisms of the cells of the gut?

A
  • natural loss
  • DNA monitors
  • repair enzymes.
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7
Q

what is a polyp?

A
  • any projection from a mucosal surface into a hollow viscus, and maybe hyperplastic, neoplastic, inflammatory, hamartomatous.
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8
Q

what are the types of colonic polyps?

A

-they can be :

  • Metaplastic/hyperplastic
  • Adenomas - Juvenile, Peutz Jeghers, lipomas (less common)
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9
Q

define adenoma:

A

benign neoplasm of the mucosa.

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10
Q

what are hyperplastic polyps?

how common are they?

how many have mutations?

A
  • very common growths
  • Constitute 90% of all colon polyps
  • there are often multiple
  • they have no malignant potential
  • 15% has a K- Ras mutation
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11
Q

what are colonic adenoma types?

A
  • 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
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12
Q

what is the anatomy of the adenoma?

A
  • 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
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13
Q

what is the microstructure of tubular adenomas?

A
  • Columnar cells with nuclear enlargement, elongation and multi-layering and loss of polarity. - Proliferation. - Reduced differentiation. - Complexity/disorganisation of architecture.
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14
Q

what is the microstructure of villous adenomas?

A
  • Mucinous cells with nuclear enlargement, elongation, multi-layering, and loss of polarity
  • Exophytic -frond-like extension
    *
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15
Q

what is dysplasia?

A

abnormal growth of cells with same features of cancer - categorised into indefinite, low grade and high grade

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16
Q

what is FAP?

A
  • 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
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17
Q

what do patients with FAP undergo?

A
  • prophylactic colectomy
18
Q

how many adults have adenomas at 50?

how many of these adenomas might become cancerous?

A
  • 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.
19
Q

do larger or smaller polyps have a greater chance of becoming Colonic Adenomas?

A

larger polyps

20
Q

what are the genetic pathways in colorectal cancer?

A
  • Adenoma Carcinoma Sequence
  • Microsatellite Instability
  • Genetic predisposition for colorectal cancer
21
Q

explain the adenoma-carcinoma sequence?

A
  • if the gene APC is damaged it can lead to colorectal cancer
22
Q
  • what are microsites?
  • what is microsatellite instability?
A
  • Microsatellites are repeat sequences that are prone to misalignment
  • some microsatellites are in coding sequences of genes which inhibit growth or apoptosis
23
Q

what is mismatch repair genes?

what is HNPCC?

A
  • 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
24
Q

what are the main genetic pathways leading to colorectal cancer?

A
  • FAP – inactivation of APC TSG.

HNPCC – microsatellite instability

25
Q

why is APC so important in colon cancer?

A
26
Q

in which countries is colorectal cancer common?

which countries is colorectal cancer not common?

A
  • High in USA, Eastern Europe and Australia
  • Low in Japan, Mexico and Africa
27
Q

which dietary factors pre dispose to colorectal cancer?

A
  • high fat
  • low fibre
  • high red meat
  • refined carbohydrates.

these are all food which increase the likelihood of colorectal cancer

28
Q

how does high temperature affect foods?

A

High temperature cooking can modify chemicals further in food and induce mutagenic chemicals.

29
Q

which food deficiencies might lead to colorectal cancer?

A
  • a deficiency in folate and MTHFR
30
Q

why does a deficiency of folate increase chance of colorectal cancer?

A
  • Folates are important co=enzymes for nucleotide synthesis and DNA

methylation

31
Q

why does a deficiency in MTHFR increase risk of colorectal cancer?

A
  • Deficiency leads to disruption in DNA synthesis causing DNA instability and this leads to mutation
  • Decreased methionine synthesis leads to genomic hypomethylation and focal hypermethylation (this can have gene activating and gene silencing effects)
32
Q

which foods have anti carcinogenic elements?

A
    • Vitamin C and E
    • ROS scavengers.
    • Polyphenols
  • – green tea and fruit juice.
  • Isothiocyanates
  • – cruciferous vegetables
33
Q

what is the clinical presentation of colorectal cancer?

A
  • Change in bowel habit. - Pre-rectal bleeding - Unexplained iron deficient anaemia - mucus pre-rectal production - bloating - cramps - weight loss and fatigue.
34
Q

what are the macroscopic features of colorectal cancer?

A
  • Small carcinomas may be present within larger polypoid adenomas
35
Q

what is the distribution of where carcinomas appear within the colon?

A
  • Caecum/Ascending Colon = 22%
  • Transverse Colon = 11%
  • Descending Colon = 6%
  • RECTOSIGMOID = 55%
36
Q

what are the microscopic features of carcinomas?

A
    • Almost all are adenocarcinomas.
  • Mucinous carcinoma (type of
  • Signet ring cell carcinoma.
  • Neuroendocrine carcinoma (rare).
37
Q

how can colorectal cancer be graded?

A
  • we can grade CRC by the proportion of gland differentiation
  • we use dukes classification

10% are well differentiated\

70% are moderately differentiated

38
Q

what are the stages of Dukes classification?

A
  • Dukes A

Growth limited to the wall (muscularis propria)

Nodes negative

  • Dukes B

Growth beyond muscularis propria

Nodes negative

  • Dukes C1

Nodes are positive

Apical lymph node negative

  • Dukes C2
39
Q

what clinical features affect prognosis?

A
  • Diagnosis of asymptomatic patients
  • Rectal bleeding as presenting symptom (improves prognosis) o Bowel obstruction (diminished prognosis)
  • Tumour location
  • Age < 30 (diminished prognosis)
  • Preoperative serum CEA (carcinoembryonic antigen) (diminished prognosis with high CEA)
  • Distant metastases (markedly diminished prognosis)
40
Q

which pathological features affect the prognosis of colorectal cancer?

A
  • Depth of bowel wall penetration (increased penetration = diminished
  • prognosis)
  • Number of regional lymph nodes involved
  • Degree of differentiation
  • Mucinous (colloid) or signet ring cell (diminished prognosis) o Lymphatic invasion (diminished prognosis)
  • Venous invasion (diminished prognosis)
  • Perineural invasion (diminished prognosis)
  • Local inflammation and immunologic reaction (improved prognosis)
41
Q

what are the criteria for screening for colorectal cancer?

A
  • Previous adenoma
  • 1st degree relative affected by colorectal cancer before the age of 45
  • 2 affected first degree relatives
  • Evidence of dominant familial cancer trait including colorectal, uterine, and other cancers
  • Ulcerative colitis and Crohn’s disease
  • Hereditable cancer families (include other sites)
42
Q

what does the NHS screening for colon cancer consist of?

A
  • They look for Faecal Occult Blood (FOB)
  • From 55 years onwards they will send a FOB test kit
  • if there is blood present an endoscopy is performed

55-60 = sigmoidoscopy

>60 = full colonoscopy

Year 2 - Cancer (15 decks)

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