Colorectal Cancer (CRC)

Snapshot

• A 68-year-old man presents to his primary care physician for fatigue. He reports a change in his bowel habits and noticed his stool is pencil thin. He also endorses an unintentional 20-pound weight loss over the course of 2 months. His father died of colon cancer when he was 65 years of age. He has never had a colonoscopy. Physical examination is notable for tenderness upon palpation in the left abdomen. Laboratory studies are notable for iron deficiency anemia. 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
  • may be associated with an increased CEA 
• 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
• 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 
  • 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

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

Complications

• Colonic obstrucition
• Bowel perforation
• Metastasis