Colorectal Cancer (CRC) - Oncology

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

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T