Updated: 12/27/2021

Colorectal Cancer

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  • Snapshot
    • A 66-year-old man presents to his primary care physician for a routine exam. He reports a change in his bowel habits and noticed his stool is pencil thin. He also endorses an unintentional 15-pound weight loss over the course of 1 month. His father died of colon cancer when he was 65 years of age. Physical examination is notable for tenderness upon palpation in the left abdomen. Colonoscopy is notable for a colonic mass in the descending colon.
  • Introduction
    • Overview
      • describes malignancy affecting the colon or rectum
      • most colorectal cancer arises from an adenomatous polyp
  • Epidemiology
    • Incidence
      • incidence has decreased due to improved screening practices (e.g., colonoscopy)
    • Demographics
      • typically seen in ≥ 60 years of age
      • men > women
    • Risk factors
      • hereditary syndromes
        • Lynch syndrome (hereditary nonpolyposis colorectal cancer)
        • familial adenomatous polyposis
        • MYH-associated polyposis
      • environmental factors
        • diets high in animal fat
      • inflammatory bowel disease
        • ulcerative colitis
        • Crohn disease
      • cigarette smoking
  • ETIOLOGY
    • Pathogenesis
      • chromosomal instability pathway
        • APC/β-catenin gene mutation
          • initiating event in adenoma formation
          • leads to the formation of an aberrant crypt foci
        • KRAS mutation
          • leads to unregulating intracellular signaling resulting in adenoma formation
        • p53 and DCC gene mutation
          • results in tumorgenesis and invasive cancer
      • microsatellite instability pathway
        • mismatch repair genes
          • abnormal methylation or mutations leads to cancer development in patients with Lynch syndrome and certain sporadic colorectal cancers
    • Associated conditions
      • Streptococcus gallolyticus (previously known as Streptococcus bovis)
        • although rare, can present with this bacteremia
  • Presentation
    • Clinical presentation depends on the location of the colorectal cancer
    • Symptoms/physical exam warranting colonoscopy
      • asymptomatic
        • these patients can be found to have colorectal cancer upon routine screening
      • change in bowel habits
        • typically seen in cancer affecting the descending colon
      • rectal bleeding
        • typically seen in rectal cancers
      • rectal or abdominal mass
      • unexplained iron deficiency anemia
        • secondary to gastrointestinal bleeding
        • typically seen in cancer affecting the ascending colon
      • malaise, unintentional weight-loss, and fatigue
      • age > 50 years
      • sudden and unprovoked deep vein thrombosis
  • Imaging
    • Colonoscopy
      • indication
        • to visualize the colonic mucosa and obtain a biopsy from colonic mass to establish a histologic diagnosis
        • gold standard for evaluating for colorectal cancer
        • screening method
          • low-risk patients
            • screen at 50 years of age
              • continue performing every 10 years
          • first-degree relative with colon cancer
            • screen at 40 years of age or 10 years prior to the relatives age of presentation
          • for patients who do not want to undergo colonoscopy, other screening options include
            • fecal immunochemical test (FIT)
              • assesses for ocult blood in the stool
            • computed tomography colonography
  • Differential
    • Diverticulitis
      • differentiating factors
        • inflammation of the diverticula
  • Treatment
    • Treatment is geared towards the staging of the malignacy
    • Surgical
      • resection
        • indication
          • performed in localized disease
            • typically given with adjuvant chemotherapy
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