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PATIENT STORY

A 72-year-old man reports rectal bleeding with bowel movements over the past several months and the stool seems narrower with occasional diarrhea. He has a history of hemorrhoids but now is not experiencing rectal irritation or itching, as with previous episodes. His medical history is significant for controlled hypertension and a remote history of smoking. On digital rectal examination, his stool sample tests positive for blood but anoscopy fails to identify the source of bleeding. On colonoscopy, a mass is seen at 30 cm (Figure 66-1). A biopsy was obtained and pathology confirmed adenocarcinoma.

FIGURE 66-1

A sessile colon mass seen at 30 cm. At surgery, this was found to be a Duke stage A adenocarcinoma. (Reproduced with permission from Michael Harper, MD.)

INTRODUCTION

Colorectal cancer (CRC) is a malignant neoplasm of the colon, most commonly adenocarcinoma. There has been a slow decline in both the incidence and mortality from colon cancer, although it is the second leading cause of cancer death in the United States.1

EPIDEMIOLOGY

  • In 2013, 136,119 people in the United States were diagnosed with CRC and there were 51,813 associated deaths.1

  • Incidence increases with age and is higher in men than women.1 Of every 100 men who are 60 years old today, 1 to 2 will get colorectal cancer by the age of 70 years. Of every 100 women who are 70 years old today, 1 to 2 will get colorectal cancer by the age of 80 years.1

  • Colon carcinoma rates are higher in blacks than in whites and lowest among American Indians and Alaska Natives.1

  • Individuals with a first-degree relative with CRC were at slightly increased risk of developing CRC (hazard ratio [HR], 1.23; 95% confidence interval [CI], 1.07–1.42); risk was higher in those with 2 or more first-degree relatives with CRC (HR, 2.04; 95% CI, 1.44–2.86).2

ETIOLOGY AND PATHOPHYSIOLOGY

  • Colon cancer appears to be a multipathway disease with tumors usually arising from adenomatous polyps or serrated adenomas; mutational events occur within the polyp, including activation of oncogenes and loss of tumor-suppressor genes.3

  • The probability of a polyp undergoing malignant transformation increases for the following cases4:

    • The polyp is sessile, especially if villous histology or flat.

    • Larger size—Malignant transformation is rare if smaller than 1.5 cm, 2% to 10% if 1.5 to 2.5 cm, and 10% if larger than 2.5 cm.

  • Serrated polyps are associated with an increased risk of detection of synchronous advanced neoplasia (odds ratio 2.05; 95% CI, 1.38–3.04).5

  • Strong associations with CRC risk are found in eight variants of five genes (adenomatous polyposis coli [APC], CHEK2, DNMT3B, MLH1, and MUTYH), moderate associations for two variants in two genes (GSTM1 and TERT), and weak ...

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