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wassupp loser > imaging - colorectal cancer > Flashcards

imaging - colorectal cancer Flashcards

1
Q

what is colorectal cancer?

A

this type of cancer begins in the cells of colonic
crypts and spreads first through the wall of the colon and potentially into the lymphatic system and other organs.
basically cancer beginning in the colon and/or rectum

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2
Q

what is the most common type of colorectal cancer?

A

adenocarcinoma

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3
Q

what are the 3 most common cancers in singaporean men and women respectively?

A

men:
1. colorectal
2. lung
3. prostate

women:
1. breast
2. colorectal
3. lung

note: colorectal cancer is the 3rd most common cause of cancer death amongst males and females in Singapore

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4
Q

what are some of the causes/ risk factors of colorectal cancer?

A

modifiable:
- smoking
- diet: low-fibre, high red meat diet
- alcohol
- lifestyle: sedentary lifestyle, obesity

non-modifiable:
- age (older -> higher risk)
- gender (male)
- medical history (colorectal polyps, inflammatory bowel disease- Crohn’s, ulcerative colitis -> IBD is chronic inflammation, so promotes accumulation of mutations)
- family history
- genetics (APC, mismatch repair genes)

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5
Q

what are some specific single-gene defect genetic risk factors for colorectal cancer?

how do these fit into the hallmarks of cancer?

A
  • familial adenomatous polyposis (FAP): autosomal dominant syndrome, caused by germline loss-of-function mutations in the APC gene (a tumour suppressor gene) -> since FAP involves growth of multiple colon and rectal polyps
    FAP- very high risk of developing colorectal cancer if don’t undergo colectomy
    hallmark: evasion of growth inhibitory signals
  • hereditary non-polyposis colorectal cancer (HNPCC) (lynch syndrome): caused by mismatch of genes responsible for DNA repair (ie. MMR mutation in MSH6 MSH2) (ie. mismatched repair genes)
    note- HNPCC also increases risk of endometrial, ovarian and stomach cancers
    hallmark: genome instability
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6
Q

what is the pathogenesis of most colorectal cancers?

A
  • most colorectal cancers arise from benign growths, adenomatous polyps
  • the adenomatous polyps may arise due to genetic mutations, or alterations in the epithelial cells that line the inner surface of the colon or rectum
  • overtime: accumulation of mutations -> uncontrolled cell growth and proliferation -> (possibly) dysplasia, metaplasia
  • formation of malignant tumours
  • as cancer progresses: invasion, metastasis, angiogenesis
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7
Q

what are some common sites of metastasis of colorectal adenocarcinoma?

A

liver
lungs
peritoneum
regional lymph nodes - eg. mesenteric LNs, iliac LNs, pararectal LNs, pericolic LNs

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8
Q

what are some gross features of colorectal cancer?

A
  • polypoidal (not in HNPCC), fungating and/or ulcerated appearance
  • larger tumors predominated in the proximal colon
  • circumferential growth or apple core lesions more common in distal colon (annular, encircling lesions, constricts and obstructs bowel)
  • invasion of surrounding structures?
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9
Q

what are some histological features of colorectal adenocarcinoma?

A
  • usually poorly differentiated
  • lymphocytic infiltration
  • nuclear pleomorphism
  • prominent nucleoli
  • high nucleus: cytoplasm ratio
  • possibly: signet ring cells (vv aggressive cancer!)
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10
Q

what are some signs and symptoms of colorectal cancer?

A
  • loss of weight, loss of appetite
  • for proximal colon cancers: melena, iron-deficiency anemia
  • for distal colon cancers: hematochezia (rectal bleeding)
  • altered bowel habits (incl. pencil thin stools)
  • abdominal pain
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11
Q

what are some investigations and findings involved in the diagnosis of colorectal carcinoma?

A
  • physical examination: abdominal tenderness, palpable masses, signs of anemia
  • colonoscopy: to find any abnormal growths (polyps)
  • biopsy
  • lab tests: low RBC, tumour markers
  • genetic testing (for FAP and lynch syndrome)
  • imaging:
    • CT, MRI, PET scan
      -CT espeically used to see metstasis for eg. liver mets –> multiple diffuse nodular HYPOdensities ie. appear DARKER
      • recall CT: bones are bright white (hyperdense)
    • X-ray (with barium enema): apple-core lesion (may also be seen in CT colonography)
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12
Q

describe the apple core lesion/napkin ring sign

A
  • focal narrowing of the colon with an eccentric/asymmetrical luminal contour

ie. intestinal obstruction causing the focal narrowing, with dilation of intestines proximal to the mass

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13
Q

why does colorectal cancer cause apple core lesion?

A

due to a constriction of the lumen of the colon by a stenosing annular colorectal carcinoma, causing the narrowing of the lumen and only allowing a small amount of contrast medium to enter (and possibly- dilation of bowel proximal to lesion)

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14
Q

what are some other possible causes of apple core lesion?

A
  • Crohn’s disease
  • chronic ulcerative colitis
  • ischemic colitis
  • etc
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15
Q

what are some complications of colorectal cancer?

A

intestinal obstruction
dilation of intestines proximal to the mass

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16
Q

what are the key screening methods for colorectal cancer?

A
  • genetic testing (especially for individuals with significant family history)
  • for average individuals above 50 years old:
    • annual FIT (faecal immunochemical test- test for presence of blood in stool)
  • colonoscopy (more invasive!) - once every 5-10 years
  • for individuals with higher risk (eg. positive family history):
    • colonoscopy once every 5 years (first-degree relative)
  • colonoscopy ~ once a year (if positive history of FAP, HNPCC) (or have IBD - start around 10 years after diagnosis)
17
Q

how is colorectal cancer staged? why is staging important?

A

TNM classification:
T- invasion beyond muscularis mucosae (instead of basement membrane- still carcinoma in situ)
N- based on how many LNs invaded (1-3: N1)
M: based on how many distant organs it has spread/metastasised to

staging- important indicator for prognosis (and hence guides patient counselling)

18
Q

what is inflammatory bowel disease?

A

chronic condition resulting from inappropriate mucosal immune activation

includes Crohn’s and chronic ulcerative colitis

19
Q

what are some differences between Crohn’s and ulcerative colitis (UC)?

A
  • Crohn’s involves ileum and/or colon, while UC only involves the colon
  • Crohn’s involves skip lesions, UC involves diffuse continuous lesions
  • Crohn’s involves transmural inflammation, UC involves mucosal inflammation
  • Crohn’s involves deep, knife-like ulcers, UC involves superficial broad-based ulcers
  • Crohn’s may have granulomas, UC does not have granulomas
20
Q

what is grading of cancers? what is the importance?

A

grading is based on the degree of cellular differentiation (eg. cellular pleomorphism, nuclear pleomorphism, irregularly-shaped nucleus, high nucleus to cytoplasm ratio, prominent nuclei, hyperchromatism, presence of mitotic figures)

mainly informs of aggressive and malignancy -> aids in medical decision making

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