Colorectal Carcinoma Notes

Overview of Colorectal Carcinoma
  • Arises from colonic or rectal mucosa.
  • Peak incidence: ages 60 to 70.
  • Third most common cancer (excluding skin) and third leading cause of cancer-related deaths.
Molecular Mechanisms of Colorectal Carcinoma
  • Two major pathways:
    1. Adenoma-Carcinoma Sequence
    • The most common pathway, accounting for ~80% of colorectal cancers.
    • Involves progression from adenoma (benign polyp) to carcinoma.
    1. Microsatellite Instability (MSI) Pathway
    • Involves defects in DNA mismatch repair enzymes leading to instability in microsatellites (repeating non-coding DNA sequences).
    • Major example: Hereditary Non-Polyposis Colorectal Carcinoma (HNPCC).
      • Inherited mutation in DNA mismatch repair enzymes.
      • Increased risks for colorectal, ovarian, and endometrial carcinomas.
Additional Risk Factors
  • Ulcerative Colitis:
    • Chronic inflammation increases risk for colorectal cancer.
  • Peutz-Jeghers Syndrome:
    • Associated with increased risk for colorectal carcinoma.
Screening for Colorectal Carcinoma
  • Common methods:
    1. Colonoscopy
    • Correcting the transcript from "endoscopy" to "colonoscopy".
    • Aims to remove adenomatous polyps before they become cancerous.
    1. Fecal Occult Blood Testing
    • Detects bleeding from polyps or cancers, ideally screening begins at age 50.
Characteristics of Colorectal Carcinoma
  • Cancer can occur anywhere along the colon:
    • Left-Sided Carcinoma:
    • Grows as a napkin ring lesion affecting the bowel lumen, leading to:
      • Decreased stool caliber (pencil-thin stools).
      • Left lower quadrant pain.
      • Possible blood streaking in stool.
    • Right-Sided Carcinoma:
    • Grows as a raised lesion on the surface of colonic mucosa.
    • Symptoms include:
      • Iron deficiency anemia due to chronic blood loss.
      • Vague abdominal pain.
Associated Conditions
  • Streptococcus bovis Endocarditis:
    • Increased association with colorectal carcinoma.
    • Important for clinical examination when noted in endocarditis patients.
Staging of Colorectal Carcinoma
  • T Stage: Depth of invasion into the bowel wall.
  • N Stage: Involvement of regional lymph nodes.
  • M Stage: Distant spread, most commonly to the liver.
Tumor Markers
  • Carcinoembryonic Antigen (CEA):
    • Not useful for screening but important for:
    • Assessing treatment response (decrease after effective treatment).
    • Detecting recurrence (elevated levels may indicate return of disease).