Carcinoma arising from the epithelial lining of the colon or of the rectum
Most colorectal cancers arise from adenomatous polyps
Strongly linked to age, with 83% occurring in people ≥60 years old
Rectal cancer is defined as cancerous lesions located within 12 cm of the anal verge (with rigid proctoscopy)
Epidemiology
An estimated 1.9 million incident cases per year is reported globally
Incidence is higher in males
Most frequently occurring in middle- to high-income countries
Third most common cancer and second leading cause of cancer death globally
Signs and Symptoms
Right-sided colonic lesions may present as:
Vague abdominal pain
Weight loss
Anemia secondary to chronic blood loss
Weakness
Abdominal mass
Left-sided colonic lesions may present as:
Colicky abdominal pain
Changes in bowel habits (constipation alternating with diarrhea) or narrowing of stools
Obstructive symptoms like nausea and vomiting
Lesions in the rectum may present as:
Changes in bowel habits
New onset or recurrent or persistent rectal bleeding
Rectal urgency or fullness
Tenesmus
Risk Factors
Age: Chances are increased markedly after the age of 50
Race: Colorectal cancer incidence and mortality rates are highest among African-Americans
Personal history of colorectal cancer: Chances of developing new cancers in other parts of the colon or rectum is still possible even after removal of previous colorectal cancer; risk is increased in those who had their first colorectal cancer at a young age
Personal history of colorectal polyps: Adenomatous polyps, especially multiple, large ones (>2 cm has a reported 40% chance of malignant transformation), increase the risk of developing colorectal cancer
Malignant transformation is higher for villous and tubulovillous adenomas
Familial adenomatous polyposis: Approximately 95% of FAP patients will develop adenomas by age 35 and if left untreated, has 100% chance of developing colorectal cancer
Hereditary nonpolyposis colorectal cancer or hereditary nonpolyposis colorectal cancer (Lynch syndrome): Transmitted as an autosomal dominant trait
Amsterdam II criteria identify high-risk families suspected of having hereditary nonpolyposis colorectal:
Colorectal cancer affecting ≥2 generations
≥3 relatives with a histologically diagnosed hereditary nonpolyposis colorectal-associated cancer (eg colorectal cancer, small bowel, endometrial, renal pelvis or ureteral cancer)
≥1 colorectal cancers diagnosed at <50 years of age
In suspected Lynch syndrome without a known familial mutation, first step in genetic diagnosis is identifying microsatellite instability in tumor cells
Personal history of inflammatory bowel disease (ulcerative colitis, Crohn’s disease): Increases risk for colorectal cancer; colorectal screening should be done more frequently
Risk of colorectal cancer in a patient with ulcerative colitis depends on extent of colitis, duration of active disease and symptoms, development of mucosal dysplasia
Risk of colorectal cancer in Crohn’s disease is also increased but to a lesser extent
In patients with ulcerative colitis, overall incidence of colorectal cancer is 3.7%, with 2% probability by 10 years, and 8% by 20 years
In patients with Crohn’s colitis, risk for colorectal cancer is similar while it appears that there is no significant risk associated with proctitis
Family history of colorectal cancer: Risk is highest in those with >1 affected first-degree relative (parent, siblings) or in those whose first-degree relative had colorectal cancer at a young age
Type 2 diabetes mellitus: Increases the risk of colorectal cancer and tends to have a less favorable prognosis
Diet: Consumption of red and processed meats, fat and cholesterol-rich diets have been linked to an increased risk of colorectal cancer
Heavy alcohol consumption: Increased risk of colorectal cancer is probably due to low levels of folic acid among heavy drinkers
Obesity
Both overweight and obese people are at increased risk of colorectal cancer
Pattern of fat distribution relates to the colorectal cancer risk (abdominal obesity being a stronger risk factor than truncal obesity or BMI)
Obesity approximately increases by 2 times the risk of adenomas (particularly, ≥1 cm, tubulovillous adenomas)
Smoking: Studies of recent years have found association between smoking and colorectal cancer, with relative risks between 1.5-3
