colorectal%20cancer
COLORECTAL CANCER
Colorectal cancer is a carcinoma arising from the luminal surface of the colon.
It is the 2nd most common cancer in women and third most common cancer in male worldwide. It commonly arises from adenomatous polyps.
It is strongly linked to age with 83% occurring in people ≥60 years old.
Rectal cancer is defined as cancerous lesions located within 12 cm of the anal verge.

Definition

Colorectal Cancer

  • Carcinoma arising from the epithelial lining of the colon or of the rectum
  • Incidence is higher in males
  • Strongly linked to age, with 83% occurring in people >60 years old
  • Rectal cancer is defined as cancerous lesions located within 12 cm of the anal verge (with rigid proctoscopy)

Signs and Symptoms

  • Right-sided colonic lesions may present as:
    • Vague abdominal pain
    • Weight loss
    • Anemia secondary to chronic blood loss
    • Weakness
    • Abdominal mass
  • Left-sided colonic lesions may present as:
    • Colicky abdominal pain
    • Changes in bowel habits (constipation alternating with diarrhea) or narrowing of stools
    • Obstructive symptoms like nausea & vomiting
  • Lesions in the rectum may present as:
    • Changes in bowel habits
    • New onset or recurrent or persistent rectal bleeding
    • Rectal urgency or fullness
    • Tenesmus

Risk Factors

  • Age - chances are increased markedly after the age of 50
  • Race - colorectal cancer incidence & mortality rates are highest among African-Americans
  • Personal history of colorectal cancer - chances of developing new cancers in other parts of the colon or rectum is still possible even after removal of previous colorectal cancer; risk is increased in those who had their first colorectal cancer at a young age
  • Personal history of colorectal polyps - adenomatous polyps, esp multiple, large ones (>2 cm has a reported 40% chance of malignant transformation), increase the risk of developing colorectal cancer
    • Malignant transformation is higher for villous & tubulovillous adenomas
  • Familial adenomatous polyposis - approx 95% of FAP patients will develop adenomas by age 35 & if left untreated, has 100% chance of developing colorectal cancer
  • Hereditary nonpolyposis colorectal cancer or hereditary nonpolyposis colorectal cancer (Lynch syndrome) - transmitted as an autosomal dominant trait
    • Amsterdam II criteria identify high-risk families suspected of having hereditary nonpolyposis colorectal:
      • Colorectal cancer affecting ≥2 generations
      • ≥3 relatives with a histologically diagnosed hereditary nonpolyposis colorectal-associated cancer (eg colorectal cancer, small bowel, endometrial, renal pelvis or ureteral cancer)
      • ≥1 colorectal cancers diagnosed at <50 years of age
    • In suspected Lynch syndrome without a known familial mutation, 1st step in genetic diagnosis is identifying microsatellite instability in tumor cells
  • Personal history of inflammatory bowel disease (ulcerative colitis, Crohn’s disease) - increases risk for colorectal cancer; colorectal screening should be done more frequently
    • Risk of colorectal cancer in a patient with ulcerative colitis depends on extent of colitis, duration of active disease & symptoms, development of mucosal dysplasia
    • Risk of colorectal cancer in Crohn’s disease is also increased but to a lesser extent
    • In patients with ulcerative colitis, overall incidence of colorectal cancer is 3.7%, with 2% probability by 10 years, & 8% by 20 years
    • In patients with Crohn’s colitis, risk for colorectal cancer is similar while it appears that there is no significant risk associated with proctitis
  • Family history of colorectal cancer - risk is highest in those with >1 affected first-degree relative (parent, siblings) or in those whose first-degree relative had colorectal cancer at a young age
  • Type 2 diabetes mellitus - increases the risk of colorectal cancer & tends to have a less favorable prognosis
  • Diet - fat & cholesterol-rich diets have been linked to an increased risk of colorectal cancer
  • Heavy alcohol consumption - increased risk of colorectal cancer is probably due to low levels of folic acid among heavy drinkers
  • Obesity
    • Both overweight & obese people are at increased risk of colorectal cancer
    • Pattern of fat distribution relates to the colorectal cancer risk (abdominal obesity being a stronger risk factor than truncal obesity or BMI)
    • Obesity approximately increases by 2x the risk of adenomas (particularly, ≥1 cm, tubulovillous adenomas)
  • Smoking - studies of recent years have found association between smoking & colorectal cancer, with relative risks between 1.5-3
  • Sedentary lifestyle
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