Colorectal Cancer

Question 0

CRC Pathophysiology

Answer 0

• normal colon
• > hyperproliferative epithelium
• > adenoma
• > carcinoma

Question 1

Colorectal Cancer Aetiology

Answer 1

• environmental influences: high dietary fat, low dietary fibre
  
  • genetic influences:
    
    • all colorectal cancers considered to have genetic component, to varying degrees
    • genetic changes implicated:
      
      • activation of proto-oncogenes (K-ras)
      • loss of tumour-suppressor gene activity (APC, DCC)
      • abnormalities in DNA repair genes (hMSH2, hMLHl), especially HNPCC syndromes

Question 2

CRC Risk Factors

Answer 2

• 75% have no known risk factors
  
  • age
  • adenomatous polyps
  • family history
  • IBD

Question 3

CRC Age Risk Factor

Answer 3

• 90% of cancers are in people >50 yrs old

* at age 50, the risk of developing colorectal cancer by age 80 is 5%

Question 4

CRC Family History Risk Factor

Answer 4

• sporadic cancer
  * risk increases 1.8x for those with one affected relative, 2-6x with two affected relatives
  * risk is greater if relative has cancer diagnosed < 45 yrs old
  • FAP (familial adenomatous polyposis) and Gardner’s syndrome
  • HNPCC (hereditary nonpolyposis colorectal cancer) or Lynch syndrome

Question 5

CRC IBD Risk Factor

Answer 5

• UC - after 10 yrs, cancer risk increased approximately by 1% for each additional year
  
  • Crohn’s disease - unclear, likely similar to UC if more than 1/3 of colon inflammed

Question 6

CRC Prevention

Answer 6

• Lifestyle modifications
  
  • ASA
  • Screening - Average risk and above-average risk

Question 7

CRC Lifestyle Modifications

Answer 7

• increase fibre in diet
  
  • decrease animal fat and red meat
  • decrease smoking and EtOH
  • increase exercise
  • decrease BMI

Question 8

CRC Screening for at average risk individuals

Answer 8

• > 50 years with no family history
  • FOBT q2yrs
  • Colonoscopy q10yrs

Question 9

CRC Screening for above average risk individuals

Answer 9

• HNPCC
  * Genetic testing + colonoscopy q2yrs beginning at age 20
  • FAP
    
    • Genetic testing + sigmoidoscopy annually beginning at age I0-12
  • Fam Hx of cancer
    
    • (1+ 1st degree relatives with CRC i.e. parent, sibling or child) or polyps but does not fit criteria for HNPCC/FAP
    • colonoscopy q5yrs beginning at age 40 or 10yrs earlier than the youngest diagnosed polyp/cancer case in the family.

Question 10

CRC Staging and 5 year Prognosis

Answer 10

• Dukes Staging with 5 year survival
  * Dukes A (limited to submucosa): 80-95%
  * Dukes B (penetrating serosa): 55-67%
  * Dukes C (into lymph nodes): 30-45%
  * Dukes D (metastases): 1%

Question 11

CRC Treatment

Answer 11

• Surgery
  * surgery (indicated in potentially curable or symptomatic cases- not usually in stage IV)
  • Radiotherapy and Chemotherapy
    
    • alone not curative
  • Surveillance
    
    • When polyps are found
    • Colonoscopy 3 yrs after initial finding and then q5yrs
  • Past CRC
    
    • Colonoscopy q3-5yrs