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*Medicine: Gastrointestinal > Colorectal Polyps and Neoplasms > Flashcards

Colorectal Polyps and Neoplasms Flashcards

1
Q

Rectal bleeding is bright red blood passed around or with the stool. It is extremely common and becomes more so with age.

Give a differential diagnosis for a patient with rectal bleeding

A
  • haemorrhoids
  • colorectal polyps or cancer
  • anal fissures
  • anal fistula
  • IBD - crohn’s and UC
  • diverticulitis
  • trauma
  • coagulopathies
  • angiodysplasia
  • anorectal varices
  • proctitis
  • intussusception
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2
Q

Constipation refers to bowels which open infrequently, and the faeces are hard and often cause pain during defacation.

Give a differential diagnosis for constipation

A
  • general: pregnancy, inadequate fibre/diet, dehydration
  • metabolic/endocrine: DM, hypercalcaemia, hypothyroidism, porphyria
  • functional: dyschezia, IBS
  • drugs: opiates, aspirin, anticholinergics, ca-ch blockers, antidepressants
  • adynamic bowel: spinal cord lesions, Parkinson’s, Hirschprung’s, senility, myxoedema
  • GI: obstruction, colonic disease (carcinoma, diverticular), aganglionisis, anal fissure, prolapsed piles
  • defecatory disorders: rectal prolapse/intussusceptions, rectocoele, pelvic floor dysfunction, megarectum
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3
Q

What are adenomatous polyps?

A
  • colorectal adenomas dervied from epithelial cells lining in mucosa
  • v common, incidence increases w age
  • at 60 years they are found in approx 20% of population
  • adenomas may be sporadic or familial
  • familal adenomas occur in syndromes such as FAP
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4
Q

If a patient is found to have a polyp, does that mean they have cancer?

A
  • from naked-eye appearance: mass projecting from mucosal surface
  • term ‘polyp’ tells us nothing about its biological behaviour
  • may be benign, premalignant or malignant
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5
Q

What is meant by the following terms to describe a polyp?

  • pedunculated
  • sessile
  • tubular
  • villous
  • tubulovillous
A
  • pedunculated - attached to the normal mucosa by a stalk
  • sessile - atttached to normal mucosa by broad base
  • tubular - composed of tubular structures when looked at down microscope
  • villous - composed of finger-like projections when looked at down microscope
  • tubulovillous - contains mixture of tubular + villous architectures
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6
Q

Polyps are predominantly asymptomatic. However what are some clinical features that might be mentioned by a patient with polyps?

A
  • rectal bleeding
  • mucus discharges
  • tenesmus
  • changes in bowel habits, particularly urgency
  • signs of anaemia
    • fatigue
  • sessile villous adenomas present with profuse diarrhoea and hypokalaemia

Many polyps are picked up incidentally when imaging is performed for other reasons

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7
Q

Are colorectal adenomas cancerous?

A
  • no - they are dysplastic by definition
  • pre-malignant, so left untreated may progress to adenocarcinoma
  • in the GI tract, dyplasia is graded as low or high
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8
Q

Majority of adenomas will not progress to adenocarcinoma during a person’s lifetime. What are features associatd with a greater risk of progression?

A
  • high grade dysplasia (rather than low grade)
  • increasing size
  • histological type (villous is higher risk than tubular)
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9
Q

Why is the term ‘adenoma’ in the GI tract confusing?

A
  • in most contexts, an adenoma is a benign tumour of glandular epithelium which does not have the potential to become cancer (ie. adenomas are not premalignant)
  • however in GI tract, term ‘adenoma’ is used for premalignant lesions
  • by definition adenomas in GI tract are dysplastic (premalignant)
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10
Q

About 70% of colorectal cancers arise as a result of a (3) stepwise progression. What is this progression?

A

normal mucosa -> adenoma -> invasive adenocarcinoma

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11
Q

What is the progession to invasive adenocarcinoma due to?

A

accumulation of mutations in a number of critical growth-regulating genes:

  • inappropriate activation of proto-oncogenes (eg. K-ras, c-myc)
  • inactivation of tumour suppressor genes (eg. APC, TP53) - remember that both copies of tumour suppressor genes must be inactivated (‘two-hit’ hypothesis) since if only one allele for the gene is damaged, the second can still produce the correct protein

the exact order in which these mutations are acquired may very; it is the accumulation of mutations rather than their occurrence in a specific order which is most critical

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12
Q

Hence, use examples of genes to describe the process occurring from normal colon to carcinoma

A
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13
Q

What are the two pathways for developing colorectal cancers?

A
  • 70%: chromosomal instability pathway (=adenoma-carcinoma pathway)
  • 30%: microsatellite instability (MSI) pathway (= serrated pathway)
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14
Q

The large majority of pts who develop colorectal cancer through the adenoma-carcinoma pathway do so by acquiring sporadic mutations during life. These pts do not have a familial syndrome.

A small minority of pts who develop colorectal cancer through the adenoma-carcinoma pathway have a germline mutation in what gene?

A
  • APC gene
  • these pts have familial adenomatous polyposis
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15
Q

What is familial adenomatous polyposis?

A
  • have germline mutation in one allele of APC gene
  • other allele is normal
  • FAP is a familial syndrome, inherited (autosomal dominant)
  • although de novo germline mutations may account for up to 25% of cases
  • affects 1 in 10,000
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16
Q

How/why do patients with FAP develop cancer?

A
  • by following adenoma-carcinoma pathway sequence
  • however, bc they have a germline mutation in the APC gene, every single cell in the body has the mutation (ie. every cell is already one step further along the pathway than in non-FAP patients)
  • they develop hundreds of adenomatous polyps throughout the large intestine during their teens + 20s - t_he risk of development of an adenocarcinoma in one of these polyps is almost 100%_ by the age of about 40
  • prophylactic panproctocolectomy is usually advised in these pts
17
Q

FAP is thought to account for less than 1% of colorectal cancers (it is less common than Lynch syndrome). What is the mean age of developing colorectal cancer in FAP patients?

A
  • 39 - compared to 70 in sporadic cases
18
Q

FAP confers an increased risk of developing small intestinal adenomas/carcinomas - where, in particular?

A
  • ampulla of Vater
19
Q

What extra-intestinal manifestations is FAP associated with?

A
  • desmoid tumours (locally aggressive tumor that does not metastasize)
  • thyroid carcinomas
  • osteomas (non-cancerous bony growths)
  • congenital hypertrophy of the retinal pigmented epithelium
20
Q

Fairly recently it has been recognised that ~30% cancers arise from an alternative pathway. What is this pathway?

A
  • Microsatellite instability pathway (=serrated pathway)
  • cancers arise from serrated polyps (also termed serrated “lesions”)
  • called serrated as they have a serrated appearance microscopically
21
Q

These serrated polyps may acquire sporadic mutations in a number of key genes, such as?

A
  • activation of BRAF (an oncogene)
  • silencing of mismatch repair genes (eg. MLH1, MSH2) due to hypermethylation of promotors. This results in microsatellite instability (MSI) - insertion or deletion of nucleotides within repeated sequences of DNA.

the accumulation of these mutations may lead to development of carcinoma

22
Q

What is Lynch syndrome?

A
  • familial syndrome, inherited (autosomal dominant)
  • up to 5% of cases may be due to de novo mutations
  • have germline mutation in one allele of a DNA mismatch repair gene
  • other allele is normal
  • a ‘second hit’ (eg. promotor methylation, second mutation) is present in the genome of tumours in patients with LS
23
Q

Lynch syndrome: The order of frequency for germline mutation in the DNA mismatch repair gene is: MSH6 (most common), MSH2, MLH1, PMS2. What are the mismatch repair genes responsible for?

A
  • recognising + repairing mistakes in DNA transcription
  • which occur particualrly in areas of repeat DNA sequences (microsatellites) where DNA polymerases have a tendency to ‘slip’, either inserting extra or removing repeats.
  • in the case of mononucleotide and dinucleotide repeat sequences this often leads to a frameshift mutation, resulting in a shortened non-functional protein
24
Q

What cancers are patients with Lynch syndrome at risk of developing?

A
  • Colorectal
  • Endometrial - in women with LS, this is more common than colorectal cancer + it is more often the first (sentinel) cancer they develop
  • Stomach
  • Pancreatic
  • Small bowel
  • Ureter
  • Renal pelvic
  • Ovarian
25
Q

Lynch syndrome is thought to account for what proportion of colorectal cancers?

A
  • ~3%
  • commonest familial syndrome associated w colorectal cancer
26
Q

How are colorectcal cancers in Lynch syndrome different from sporadic cases?

A
  • tend to arise in right-side of colon
  • more commonly poorly differentiated
27
Q

What is the liftetime risk of developing colorectal cancer in Lynch syndrome?

A
  • approx 70%
  • but varies depending on which mismatch repair gene is mutated (the risk of developing CRC is highest in MLH1 or MSH2 mutation carriers)
28
Q

What is the average age of CRC diagnosis in LS mutation carriers?

A
  • 45-50 years compared to 70 in sporadic cases
29
Q

What are the risk factors for colorectal cancer?

A
  • increasing age
  • diet - low fibre, high animal fat/meat/refined carbs
  • adenomatous polyps
  • hereditary cancer syndromes (nb. most CRCs are sporadic + occur in individuals without these syndromes)
    • familial adenomatous polyposis (FAP)
    • Lynch syndrome
30
Q

The clinical presentation of colon cancer depends to a degree on the site of the tumour. How do right-sided colon (5%) + caecal (15%) tumours present?

A
  • anaemia (bleeding)*
  • weight loss
  • right iliac fossa mass (rarely small bowel obstruction)

*right-sided colon cancers often present clinically w/ non-specific features due to iron-deficiency anaemia (eg. fatigue, weakness). This is a major reason why iron def anaemia in an older man or post-menopausal woman is GI cancer until proven otherwise.

31
Q

How do left-sided (10%) and sigmoid colon (20%) cancers present?

A
  • altered bowel habit
  • PR bleeding + mucus
  • 1/3 large bowel obstruction
32
Q

How do rectal cancers (50%) present clinically?

A
  • altered bowel habit
  • fresh blood per rectum
  • mucus per rectum
  • tenesmus
  • mass per rectum
33
Q

What emergencies might some bowel cancer patients present with?

A

30% total present as an emergency

  • 80% → obstruction
  • 15% → perforation
  • 5% → haemorrhage
34
Q

What is the staging of colon cancer?

A
35
Q

Which investigations are necessary for colorectal cancer?

A
  • FBC → microcytic anaemia
  • LFT / U+Es → baseline
  • Colonoscopy → visualises entire inner surface of large bowel + biopsy
  • Sigmoidoscopy → best for rectal and left-sided carcinomas
  • Barium enema → safe, well-tolerated, not requiring IV sedation
  • CT Tap → local and distal extent of disease
36
Q

Surgery aims to cure and may increase survival times up to 50%. In elective surgery, anastomosis is typically achieved at the first operation.

Which resections suit which sites of bowel cancer?

A
37
Q

When are radiotherapy and chemotherapy used for bowel cancer?

A
  • Radiotherapy → palliation / occasionally pre-op in rectal cancer to allow resection
  • Chemo → adjuvant for stage 3 disease
38
Q

What is the screening for bowel cancer?

A
  • Every 2 years to all men and women aged 60-74yrs
  • Patients over 74 may request screening
  • Patients sent FIT tests through post
  • It’s a type of faecal occult blood test
  • Only detects human Hb as opposed to animal Hb from diet
  • Only one sample required
39
Q

Patients with abnormal screening (FIT) results are offered a colonoscopy.

What are the statistics for these patients actually having bowel cancer?

A
  • 5 out of 10 will have a normal exam
  • 4 out of 10 will be found to have polyps which may be removed due to premalignant potential
  • 1 out of 10 will have cancer

*Medicine: Gastrointestinal (29 decks)

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