Colorectal Cancer

Key Features

Essentials of Diagnosis

• Personal or family history of adenomatous or serrated polyps or colorectal cancer are important risk factors

• Symptoms or signs depend on tumor location

• Proximal colon: fecal occult blood, anemia

• Distal colon: change in bowel habits, hematochezia

• Diagnosis established with colonoscopy

General Considerations

• Almost all colon cancers are adenocarcinomas

• Most colorectal cancers arise from malignant transformation of an adenomatous polyp (tubular, tubulovillous, or villous adenoma) or serrated polyp (traditional serrated adenoma, or sessile serrated adenoma, or less commonly, hyperplastic polyp)

• Up to 5% of colorectal cancers are caused by inherited autosomal dominant germline mutations resulting in polyposis syndromes or hereditary nonpolyposis colorectal cancer (Lynch syndrome)

• Risk factors

  • Age

    • Over the past two decades, there has been a 20% decrease in incidence among adults over age 50 (likely due to colorectal cancer screening programs)

    • However, over the same time span, there has been a 50% increase in incidence among adults under age 50 (especially in the distal colon and rectum)

    • The incidence of young adult–onset colorectal cancer is rising in all racial and ethnic groups

  • History of colorectal cancer or adenomatous polyps

  • Family history of colorectal cancer

  • Inflammatory bowel disease (ulcerative colitis and Crohn colitis)

  • Diets rich in fats and red meat

  • Race (higher risk in Blacks than in Whites)

Demographics

• Second leading cause of death due to malignancy in the United States

• Colorectal cancer will develop in 4.2% of Americans and has a 5-year survival rate of 65%

• In 2020, there were an estimated 147,950 new cases of colorectal cancer in the United States, with an estimated 53,200 deaths

• Between 1996 and 2010

  • Mortality has decreased by 46%

  • The percent of patients 50 years or older who were screened for colorectal cancer has increased to 66%

Clinical Findings

Symptoms and Signs

• Adenocarcinomas grow slowly and may be asymptomatic

• Right-sided colon cancers cause

  • Iron deficiency anemia

  • Fatigue

  • Weakness from chronic blood loss

• Left-sided colon cancers cause

  • Obstructive symptoms

  • Colicky abdominal pain

  • Change in bowel habits

  • Constipation alternating with loose stools

  • Stool streaked with blood

• Rectal cancers cause

  • Rectal tenesmus

  • Urgency

  • Recurrent hematochezia

• Physical examination usually normal, except in advanced disease

• Hepatomegaly suggests metastatic spread

Differential Diagnosis

• Diverticulosis or diverticulitis

• Hemorrhoids

• Adenomatous polyps

• Ischemic colitis

• Inflammatory bowel disease

• Irritable bowel syndrome

• Infectious colitis

• Iron deficiency due to other cause

Diagnosis

Laboratory Tests

• Complete blood count may reveal iron deficiency anemia

• Elevated liver biochemical tests, particularly the serum alkaline phosphatase, are suspicious for metastatic disease

• Fecal occult blood tests (FOBT) or fecal immunochemical tests (FIT) positive

• Combination fecal DNA panel and (FIT for stool ...