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.
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.)
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
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), ...