Updated: 3/6/2020

Colorectal Cancer (CRC)

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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
 

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(M1.ON.13.60) A 72-year-old male visits his gastroenterologist for a check-up one year following resection of a 2-cm malignant lesion in his sigmoid colon. Serum levels of which of the following can be used in this patient to test for cancer recurrence? Tested Concept

QID: 101117
1

Alpha-fetoprotein

6%

(5/83)

2

Carcinoembryonic antigen

58%

(48/83)

3

Cancer antigen 125 (CA-125)

20%

(17/83)

4

Gamma glutamyl transferase

0%

(0/83)

5

CA-19-9 tumor marker

12%

(10/83)

M 4 E

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