Colorectal Ca

Anatomic Considerations and Patterns of Spread

  • Colorectum
    • Cecum
    • Ascending colon
    • Hepatic flexure
    • Transverse colon
    • Splenic flexure
    • Descending colon
    • Sigmoid colon
    • Rectum

Peritoneal investment, bowel mobility, and lymph node drainage is different as for of the colon and rectum

  • Ascending and Descending colon
    • Posterior surfaces—> in direct contact with the retroperitoneum ==> prevent mobility ==> difficulty for surgical resection
    • Anterior and lateral surfaces —>covered with peritoneum
  • Transverse colon is completely surrounded with peritoneum and supported on a long mesentery
  • Sigmoid colon evolves distally into the rectum —> the peritoneal coverage recedes

Rectum

  • 12 to 15 cm in length
  • From the rectosigmoid junction to the puborectalis ring
  • Upper third —> peritoneum anteriorly and on both sides
  • Middle third —> moves deeper into the pelvis —> only the anterior surface is covered with peritoneum
    • This forms the posterior border of the rectouterine pouch or rectovesical space
  • Lowest third —> NO peritoneal covering —> in close proximity to adjacent structures
  • ColoRectal nodal drainage
    • Pericolic nodes
    • Mesenteric nodes
  • Colon Mesentry
    • Mobile and extensive —> complete regional LN coverage with RT is difficult but is usually well treated surgically
  • Rectum
    • Major regional groups for rectal LN can be covered within a reasonable RT field
      • Perirectal
      • Presacral
      • Internal iliac nodes

Epidemiology, Risk Factors, Hereditary Disease

Epidemiology

  • World wide, approximately 1 million new cases per year are diagnosed, with 529,000 deaths
  • Median age : 7th decade
  • Colorectal adenocarcinomas can occur any time in adulthood.
  • Factors that increase the risk of developing this disease
    • Increasing age
    • Male sex
    • Family history of colorectal cancer
    • Increasing height
    • Increasing body mass index
    • Processed meat intake
    • Excessive alcohol intake
    • Low folate consumption
  • For RECTAL Ca
    • Only
      • increasing age
      • male sex
      • excessive alcohol use
  • NSAID —> maybe preventive

Molecular Cascade

Clinical Presentation

  • Symptoms
    • Minimal or no symptoms
    • Need for screening programs in the general population
    • Nonspecific
      • Changes in bowel habits
      • Weakness
      • Intermittent abdominal pain
      • Nausea & vomiting
      • Iron deficiency anemia
      • Site of the tumor
        • Right colon
          • Often exophytic
          • Commonly associated with iron deficiency anemia <== occult blood loss
          • Recently the incidence of cancer of the right colon has increased
          • Accounts for 1/3 of large-bowel ca
        • Left colon & sigmoid colon
          • Often deeply invasive, annular
          • Obstruction
          • Rectal bleeding

Prevention and Early Detection

  • Precancursers of colon ca
    • Tubular adenomas
    • Villous adenomas
      • Risk is more than Tubular
    • Tubulovillous adenomas
  • Most colorectal cancers arise from pre-existing polyps
    • Patients with neoplastic polyps —> high risk for large bowel cancer ( 15% )
    • Polypectomy may reduce this risk ( by 80% )
    • Flexible colonoscope + endoscopic polypectomy
  • Goal of screening —> detect
    • Preinvasive polyps
    • Early invasive cancer
    • Average Risk : Screening should begin at age 50
      • Annual fecal occult blood test and/or flexible sigmoidoscopy every 5 years
      • Double contrast barium enema every 5 years
      • Colonoscopy every 10 years
    • High Risk
      • adenomatous polyps
      • history of colorectal cancer
      • first-degree relative diagnosed with colorectal cancer or adenomas
      • IBD
        • UC —> x10
      • Positive genetic testing

The Adenoma-Carcinoma Sequence

  • Benign gastrointestinal tumors
    • Polyp
      • A generic term for a localized lesion projecting above the surrounding mucosa
      • Small polyps < 5 mm
      • Hyperplastic
      • Not considered to be a precursor to cancer
    • Adenomatous polyp = adenoma
      • (important) precursor lesion to cancer
      • Arise from glandular epithelium
      • Dysplastic morphology
      • Abnormal differentiation
      • Prevalence of adenomas

Pathology and Pathways of Spread

  • Colorectum Ca arise in the mucosa
  • >90% adenocarcinomas
  • squamous cell carcinoma
  • carcinoid
  • leiomyosarcoma
  • lymphoma

Little propensity for colon cancer to spread longitudinally within the bowel wall < esophageal or gastric cancers

Patterns of spread:

  • Involvement of lymphatic channels and lymph nodes
  • Hematogenous spread
    • Lung
    • Liver

Patient Evaluation/Staging

  • Pathological confirmation of adenocarcinoma,
  • Colonoscopy
    • Extent of tumor
    • Rule out synchronous primaries
      • 3% - 5%
  • CBC
  • LFT
  • CEA ( carcinoembryonic antigen )
    • High CEA ==> poor survival
  • Abdominal and pelvic CT scan
  • CXR
  • Oligometastasis
  • PET; MRI

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Prognostic factors

  • Depth of tumor invasion into and beyond the bowel wall
  • Number of involved regional lymph nodes
  • Presence or absence of distant metastases
  • High CEA