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M104 T1 > M104 T1 L13 > Flashcards

M104 T1 L13 Flashcards

1
Q

What is the third most common cancer in women after breast and lung cancer?

A

bowel cancer

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2
Q

How common is bowel cancer in men?

A

it is the third most common cancer in men after prostate and lung cancer

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3
Q

What is the global incidence of bowel cancer?

A

High incidence in the western world; low incidence in Asia and Central Africa

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4
Q

How does bowel cancer affect men and women ratio-wise?

A

affects both equally

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5
Q

What type of disease is bowel cancer?

A

it is believed to be an environmental disease and potentially preventable

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6
Q

What is a migrational risk factor of bowel cancer?

A

Individuals who migrate from a low risk area to a high risk area increase their risk of developing bowel cancer
e.g. Japanese who migrated to the USA acquired the risk of their host country

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7
Q

What are the risk factors of bowel cancer in Western countries?

A

Foods rich in red meat & fat increase the risk of
bowel cancer
Food rich in vegetables, fruit & fibre reduces the risk
of bowel cancer by ↑ faecal bulk & reduces transit
time
Physical activity & low BMI are associated with low
risk of bowel cancer

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8
Q

What are the migrational risk factors of bowel cancer?

A

Migration
Longstanding UC
Crohn’s disease; to a lesser extend than UC
Presence of adenoma in the large bowel
Previous history of bowel cancer surgery
Family history of bowel cancer
Old age – older people are also at risk of cancer in other organs besides bowel cancer

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9
Q

What reduces the risk of bowel cancer?

A

Diet rich in high fibre, fruit & vegies

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10
Q

How does high fibre diet reduce bowel cancer?

A

By increasing the formation of short chain FAs which promote healthy gut micro-organisms and reduces the proliferation of potentially neoplastic cells
Increasing stool bulk reduces transit time and potential carcinogens in the stool have a shorter contact with the bowel mucosa
it reduces formation of secondary bile acids which are potentially carcinogenic

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11
Q

What material are most polyps in the large bowel made up of?

A

dysplastic epithelium

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12
Q

What does dysplasia literally mean in Greek?

A

dys = bad; plasis = formation

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13
Q

What is the difference between the cells that make up polyps in the large bowel and between cancerous cells?

A

the cells have morphological features of cancer but without invasion of the surrounding tissue

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14
Q

What is the difference between low and high grade dysplasia?

A

Low – early precancerous features

High - advanced precancerous features with high risk of invasion if not removed

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15
Q

How is a polyp found to be cancerous or not?

A

microscopic examination by the pathologist

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16
Q

What are the three types of polyps in bowel cancer screening?

A

benign (innocent, hyperplastic)
pre-cancerous (adenoma, dysplastic)
cancerous - if the cancer is polypoid, do not use the term polyp

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17
Q

What is the difference between the appearance of tubular and villous adenomas?

A

Tubular - has test tube-like appearance

Villous - has finger-like appearance

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18
Q

What are features of benign polyps?

A

consist of numerous goblet cells compared to normal mucosa

has a lace-like pattern

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19
Q

What is a feature of Tubulovillous adenoma?

A

has a mixture of tubular and villous features

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20
Q

What are the morphological features of the Adenoma-Carcinoma Sequence?

A

macroscopic and histological features being mirrored at genetic level where there are stepwise genetic alterations

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21
Q

What driver mutations are involved in the Adenoma-Carcinoma Sequence?

A

APC, KRAS, SMAD4, and TP53 genes

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22
Q

What is the evidence for the Adenoma - Carcinoma Sequence?

A
  • Populations with high adenoma prevalence also have a high cancer prevalence
  • the distribution of adenomas in the large bowel mirrors that of bowel cancer
  • the peak incidence of polyps pre-dates the development of cancer
  • Residual adenoma is found in most cases of early invasive cancer
  • the risk of cancer is directly related to the number of polyps
  • Programmes which follow-up patients and remove adenomas reduce the incidence of bowel cancer
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23
Q

What does the ACS state?

A

that most sporadic cancers which are not genetically determined arise from adenomas

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24
Q

What evidence is there that the distribution of adenomas in the large bowel mirrors that of bowel cancer?

A

60% of the cancer arise in the left colon and rectum most adenomas arise in this region

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25
Q

How is bowel cancer screening conducted?

A

using flexible sigmoidoscopy

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26
Q

What is an example of how the peak incidence of polyps pre-dates the development of cancer?

A

the peak age for adenomas is around 60 years

the median age for bowel cancer is 71 years

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27
Q

What is an example of how the risk of cancer is directly related to the number of polyps?

A

patients with Familial Adenomatous Polyposis have high risk of cancer

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28
Q

What is the criteria to make a diagnosis of FAP?

A

having a minimum of 100 polyps

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29
Q

How many polyps are usually in patients with FAP?

A

500 – 2500 in the large bowel

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30
Q

What is the link between FAP and cancer?

A

there is a 100% risk of development of cancer by age of 30

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31
Q

What happens to FAP patients around the age of 20?

A

they undergo a prophylactic colectomy

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32
Q

What percentage of bowel cancer cases are developed from FAP?

A

1%

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33
Q

What type of condition is FAP genetically? (HAD)

A

Hereditary autosomal dominant

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34
Q

What is the defective gene responsible for FAP, and on what CMS is it located?

A

the APC gene on CMS 5q21

35
Q

What type of protein is Adenomatous Polyposis Coli?

A

a tumour suppressor

36
Q

When do FAP patients acquire the first abnormal caustative gene?

A

when in utero as a germ cell

37
Q

How do FAP patients develop polyps?

A

when they acquire the second genetic abnormality in the somatic cells - the ‘second hit’
none at birth

38
Q

What is the effect of the second hit in FAP?

A

it paves the way for the development of polyps from a young age and throughout the teen years

39
Q

What is the Two Hit Hypothesis in Hereditary Bowel Cancer?

A

when, in FAP, the patient is born with a single genetic abnormality (first hit) and acquires the second genetic abnormality (second hit) after birth to develop adenomas then cancer

40
Q

What is the Two Hit Hypothesis in Sporadic Bowel Cancer?

A

the person acquires the two hits in somatic cells to develop adenomas then cancer

41
Q

Who proposed the two hit hypothesis and why?

A

Knudson, to explain hereditary retinoblastoma

42
Q

What is the most common primary malignant intraocular cancer in children?

A

retinoblastoma

43
Q

What is the effect of the Second Hit in FAP patients?

A

the loss of the second set of normal genetic material during the ‘second hit’ leads to loss of heterozyosity
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

44
Q

What is the effect of the first hit in FAP patients?

A

it is important in the initiation of bowel cancer

With one copy of abnormal gene, the cells are heterozygous

45
Q

What happens in the Fearon & Vogelstein model?

A

genetic abnormalities are acquired in a stepwise fashion which result in the progression from normal mucosa to adenoma to cancer

46
Q

What genetic abnormalities are associated with bowel cancer?

A 
Lynch Syndrome
(Attenuated) FAP, MAP
Familial Colorectal Cancer Type X  
Serrated Polyposis Syndrome
Hamartomatous Polyposis Syndrome
47
Q

What did Lynch Syndrome used to be known as?

A

Hereditary Non-polyposis Colorectal Cancer

48
Q

What is the criteria for Attenuated FAP?

A

less than 100 adenomas

49
Q

What cancers is lynch syndrome associated with? (SUE)

A

small bowel

50
Q

What area of the body does lynch syndrome predominantly affect?

A

the caecum and right colon

51
Q

What age group does lynch syndrome affect?

A

under 50s

52
Q

What percentage of bowel cancer cases are caused by Lynch Syndrome?

A

2-3%

53
Q

Are there any precursor polyps in Lynch syndrome?

A

no

54
Q

What conditions are routinely tested for Lynch Syndrome genetic mutations?

A

Bowel cancer from young patients and advanced cancers

whether they have a family history of cancer or not

55
Q

What are the genetics of Lynch Syndrome compared to FAP?

A

Very different
but, similar to FAP individuals, LS patients inherit the defective copy of the mismatch repair gene in utero (first hit) and acquire the second copy during life (second hit) and develop cancer

56
Q

What are the genetics of Lynch Syndrome compared to FAP?

A

During replication the DNA base pairs can mismatch e.g. Guanine – Thymine instead of GC
There are mismatch repair genes which act as ‘spell checkers’ and correct these mismatches
Without the repairs the errors accumulate and create microsatellites, which are fixed for life
this leads to expansion and contractions of these repeat nucleotides causing microsatellite instability

57
Q

What are microsatellites otherwise known as?

A

short tandem repeats

58
Q

What are the mismatch repair genes involved in Lynch Syndrome?

A

MSH2 (2p16) and MLH1 (3p21) genes - 30% of LS

PMS1 and PMS2

59
Q

What does microsatellite instability indicate in Lynch Syndrome?

A

defective mismatch repair

60
Q

What genes are routinely tested for in bowel cancer?

A

the mismatch repair genes involved in Lynch Syndrome

61
Q

What criteria is used to assess Lynch syndrome?

A

the Amsterdam Criteria

62
Q

What are the features of the Amsterdam Criteria?

A

Three or more relatives with LS-associated cancer

  • One affected patient should be a first-degree relative of the other two
  • Two or more successive generations should be affected
  • Cancer in one or more affected relatives should be diagnosed before the age of 50 years;
  • FAP should be excluded in any cases of colorectal cancer
  • Tumours should be verified by pathological examination
63
Q

What are examples of LS-associated cancer?

A 
bowel cancer 
cancer of the endometrium
small bowel
ureter 
renal pelvis
64
Q

What are the symptoms of bowel cancer?

A

Can be asymptomatic and detected during screening
Change in bowel habit - constipation alternating with diarrhoea due an obstructive cancer
Bleeding from the rectum
Anaemia especially with cancers of the caecum due to slow occult blood loss
Abdominal pain due to obstruction

65
Q

How is bowel cancer diagnosed?

A

History and clinical examination
Flexible sigmoidoscopy and colonoscopy with biopsy and histological examination
CT Colonography for patients who cannot tolerate colonoscopy
Staging CT scan for distal metastasis
MRI for rectal cancer to assess local spread

66
Q

What is the pathology of bowel cancer?

A

Histologically adenocarcinoma

Graded as well, moderate & poorly differentiated

67
Q

What is meant by the three grades of adenocarcinomas in bowel cancer?

A

Well differentiated - resembles normal colonic mucosa
Moderately differentiated (most common)
Poorly differentiated - minimal or no glandular differentiation

68
Q

What are the four main stages of tumour size in bowel cancer?

A 
T1 = Invasion of the submucosa; the muscularis propria is clear
T2= Involves of the muscularis propria without full thickness invasion – in this case  there is invasion of the inner layer and not the external layer
T3 = Invasion of the full thickness of the bowel wall but not the serosa 
T4 = the cancer has gone through the bowel wall and is present on the serosa
69
Q

What are the extra two stages of tumour size in bowel cancer?

A

T3 N1 - cancer which has invaded the full thickness of the bowel with lymph node metastasis
M1 - liver metastasis from bowel cancer

70
Q

How can bowel screening help to prevent cancer?

A

by detecting polyps before they turn into cancer

it will detect early cancers at a curable stage

71
Q

What methods can be used to screen for bowel cancer?

A

Stool test / FIT

Flexible sigmoidoscopy, Colonoscopy (ideal)

72
Q

Why are colonoscopies not performed in the UK despite being ideal?

A

it requires sedation and expertise

it is associated with 1 - 2% risk of perforation

73
Q

In what country is colonoscopy used for screening?

A

in the usa

74
Q

What methods are used to screen for bowel cancer in the UK?

A

flexible sigmoidoscopy at 55years

FIT from 60-74 year olds every two years

75
Q

What are the features of sigmoidoscopies when being used to screen for bowel cancer?

A

they detect polyps and cancers in the rectum and left colon

76
Q

What is the purpose of FIT?

A

to test for occult blood - hidden blood in the stool, not visible to the naked eye
Positive test does not mean one has bowel cancer
Haemorrhoids & inflammation can cause a positive test

77
Q

How does FIT work to test for stool?

A

using an ATBY-antigen reaction

the reagent contains an ATBY specific to human blood

78
Q

How are FITs carried out?

A

The participants receive a stool kit
The test is done in the privacy of their own home
The stool kit is send to the lab
The resultant antigen-antibody reaction is read by machine

79
Q

What might cause occult bleeding?

A

Ulcerating cancers

Trauma to large polyps due to friction with stool

80
Q

What happens after a positive stool test?

A

colonoscopy referral

81
Q

What do colonoscopies detect in patients who have had a positive FIT?

A

polyps (benign and precancerous)

early and advanced cancers

82
Q

What do colonoscopies NOT detect in patients who have had a positive FIT?

A

non-bleeding polyps / cancers

83
Q

How often are FITs repeated for patients who test negative?

A

every two years

M104 T1 (15 decks)

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