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Year 2 MCD - Cancer > Cancer as a Disease: Colorectal Cancer > Flashcards

Cancer as a Disease: Colorectal Cancer Flashcards

1
Q

What is the function of the colon?

A
  • extraction of water from faeces - elctrolyte balance
  • faecal reservoir
  • bacterial digestion for vitamin production
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2
Q

Describe the anatomy of the colon

A
  • Smooth folded mucosa with a thick muscle layer
  • Cancer type = adenocarcinoma (glandular)
  • Cells divide in the crypts (stem cells) and are shunted up
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3
Q

Describe the turnover of the colon

A

2-5m cells per minute die in the colon -> high proliferation rate (cells are vulnerable to mutation)

APC mutation PREVENTS cell loss and causes cell proliferation
- Normal protective mechanisms include – natural loss, DNA monitors & repair enzymes

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4
Q

What is a polyp?

A

any projection from a mucosal surface into a hollow viscus, and may be hyperplastic/neoplastic/inflammatory/hamartomatous.

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5
Q

What are examples of polyp types?

A
  • Metaplastic/hyperplastic
  • Adenomas
  • Juvenile, Peutz Jeghers, lipomas
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6
Q

What is an adenoma?

A

benign neoplasm of the mucosa

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7
Q

What are hyperplastic polyps?

A
  • Very common growths <0.5cm
  • Constitute 90% of all colon polyps
  • Often come in multiples
  • They have NO malignant potential but 15% have a K-Ras mutation
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8
Q

What are the different types of colonic adenomas?

A
  • Tubular – 90% adenomas (>75% tubular)
  • Tubulovillous – 10% adenoma (25-50% villous)
  • Villous – (>50% villous)
  • Other – flat, serrated.

*The more villous, the worse

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9
Q

Describe the anatomy of the adenoma

A

Adenomas on a stalk – pedunculated

Flat and raised adenoma – sessile

Can both be tubular, villous

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10
Q

Describe 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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11
Q

Describe the microstructure of villous adenomas?

A
  • Mucinous cells with nuclear enlargement, elongation, multi-layering and loss of polarity
  • Exophytic – front-like extensions
  • Rarely, may hyper-secrete resulting in excess mucus discharge and hypokalaemia
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12
Q

What is APC?

A

Adenomatous Polyposis Coli
- Dysplasia
- Familial Adenomatous Polyposis (FAP):
> 5q21 gene mutation.
> Site of mutation determines clinical variants – i.e. classic, attenuated, Gardner, Turcot
- Many patients of FAP have a prophylactic colectomy

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13
Q

What is dysplasia?

A

abnormal growth of cells with same features of cancer

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14
Q

What are the main pathways to CRC?

A
  • FAP – inactivation of APC TSG

- HNPCC – microsatellite instability

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15
Q

What are microsatellites?

A

repeat sequences prone to misalignment

Some microsatellites are in coding sequences of genes which inhibit growth or apoptosis.

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16
Q

How can dietary factors predispose to colonic carcinoma?

A

high fat, low fibre, high red meat, refined carbohydrates

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

Heterocyclic Amines (HCAs) include PhIP
- PhIP (is oxidised) -> N-OH-PhIP + deoxyguanosine -> mutagenesis

Dietary deficiencies:

  1. Folates:
    - Folates are co-enzymes needed for nucleotide synthesis and DNA methylation
  2. MTHFR – Methylenetetrahydrofolate Reductase:
    - Deficiency leads to disruption in DNA synthesis causing DNA instability -> mutation
    - Decreased methionine synthesis leads to genomic hypomethylation and focal hypermethylation -> gene activating and silencing effects
17
Q

How can food have anti carconogenic elements?

A
  • Vitamin C and E – ROS scavengers
  • Isothiocyanates – cruciferous vegetables
  • Polyphenols – green tea and fruit juice
    > Can activate MAPK pathways -> regulating phase 2 metabolisms to detoxify enzymes as well as other genes and thus reduce DNA oxidation
    > EGCG-induced telomerase activity
    > Garlic associated apoptosis
18
Q

How does CRC present?

A
  • Change in bowel habit
  • Pre-rectal bleeding
  • Unexplained iron deficient anaemia
  • Other – mucus pre-rectal production, bloating, cramps (“colic”), weight loss and fatigue

*Patients & doctors rationalise these symptoms as getting old!

19
Q

What are the macroscopic features of CRC?

A

Small carcinomas may be present within larger polypoid adenomas (pedunculated or sessile)

20
Q

What are the microscopic features of CRC?

A

Almost all are adenocarcinomas

  • Mucinous carcinoma
  • Signet ring cell carcinoma
  • Neuroendocrine carcinoma (rare)
21
Q

Describe the distribution of colon cancer

A
  • Caecum/ascending colon 22%
  • Transverse colon 11%
  • Descending colon 6%
  • Recto-sigmoid 55%
22
Q

How is CRC defined?

A

by the proportion of gland differentiation relative to solid areas or nests and cords of cells without lumina

  • 10% -> Well differentiated
  • 70% -> Moderately differentiated
  • 20% -> Poorly differentiated
23
Q

What is Dukes classification?

A
  • Dukes A - growth limited to wall, nodes negative
  • Dukes B - growth beyond Muscularis propria, nodes negative
  • Dukes C1 - nodes positive, apical lymph node negative
  • Dukes C2 - apical lymph nodes (LN) positive
    > Apical lymph nodes – highest lymph node to have been removed. If +ve, chance of spread to lymph

*The scale has a worse prognosis as you go down AC2

24
Q

What clinical features affect prognosis?

A
  1. Diagnosis of asymptomatic patients = +ve
  2. Rectal bleeding as presenting symptom = +ve
  3. Bowel obstruction = -ve
  4. Tumour location = ±ve
  5. Age <30 = -ve
  6. Preoperative serum CEA (high) = -ve
  7. Distant metastasis = -ve
25
Q

What are the pathological features that affect prognosis?

A
  1. Decreased bowel wall penetration = +ve
  2. Decreased regional LN involvement = +ve
  3. Poor differentiation = -ve
  4. Mucinous/signed ring cell type = -ve
  5. Venous invasion = -ve
  6. Lymphatic invasion = -ve
  7. Peri-neural invasion = -ve
  8. Local inflammation and immunologic reaction = +ve
26
Q

What are the prequisites for CRC screening?

A
  • Previous adenoma
  • 1st degree relative affected by CRC before age 45
  • Two affected 1st degree relatives
  • Evidence of dominant familial cancer trait
  • UC and Crohn’s disease
  • Heritable cancer families
27
Q

What are the criteria for screening?

A
  • Condition should be important in respect to the seriousness and/or frequency
  • Natural history of the disease must be known – to identify where/if screening and intervention takes place
  • Test must be simple, acceptable, sensitive, selective and cost-effective
  • Screening population should have equal access to the screening procedure
28
Q

What dot hey look for in NHS screening for colon cancer?

A

for FOB – Faecal Occult Blood

*From 55+, a FOB test kit is send to people

29
Q

What happens if FOB is positive?

A

endoscopy is performed:

  • 55-60yo = sigmoidoscopy
  • 60+ = full colonoscopy

Year 2 MCD - Cancer (15 decks)

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