life

Approximately 135,000 new cases of colorectal cancer occur in the United States each year, resulting in approximately 55,000 deaths per year. Two thirds of these cases occur in the colon and one third in the rectum. The incidence and epidemiology, etiology, pathogenesis, and screening recommendations are common to both colon cancer and rectal cancer. These areas are addressed together.

Adenocarcinomas (98%) comprise most rectal cancers and are the focus of this discussion. Other rare rectal cancers, including carcinoid (0.1%), lymphoma (1.3%), and sarcoma (0.3%), are not discussed. Squamous cell carcinomas may develop in the transition area from rectum to anal verge and are considered anal carcinomas. Very rare cases of squamous cell carcinoma of the rectum have been reported.

The lifetime risk of developing a colorectal malignancy is approximately 5.9% in the general population.

Race

• Western nations tend to have a higher incidence than Asian and African countries; however, within the United States, little difference in incidence exists among whites, African Americans, and Asian Americans.
• Among religious denominations, colorectal cancer occurs more frequently in the Jewish population.

Sex

The incidence of colorectal malignancy is slightly higher in males than in females.

Age

Incidence peaks in the seventh decade; however, cases have been reported in young children

History

• All patients should undergo a complete history, including a family history and assessment of risk factors for the development of rectal cancer.
• Many rectal cancers produce no symptoms and are discovered during digital or proctoscopic screening examinations.
• Bleeding

• This is the most common symptom of rectal cancer and occurs in 60% of patients.
• Bleeding often is attributed to other causes (eg, hemorrhoids), especially if the patient has a history of other problems.
• Profuse bleeding and anemia are rare.
• Bleeding may be accompanied by the passage of mucus, which warrants further investigation.
• Change in bowel habits

• Present in 43% of patients, this symptom has several different presentations. Often, it occurs in the form of diarrhea, particularly if the tumor has a large villous component.
• These patients may have hypokalemia on laboratory studies.
• The capacity of the rectal reservoir may mask the presence of a small lesion.
• Some patients experience a change in caliber of the stool.
• Large tumors can cause obstructive symptoms.
• Tumors located low in the rectum can cause a feeling of incomplete evacuation and tenesmus.
• Occult bleeding: This is detected on screening fecal occult blood test (FOBT) in 26% of cases.
• Abdominal pain

• Partial large-bowel obstruction may cause colicky abdominal pain and bloating and is present in 20% of cases.
• Back pain is usually a late sign caused by a tumor invading or compressing nerve trunks.
• Urinary symptoms may occur if the tumor is invading or compressing the bladder or prostate.
• Malaise: This nonspecific entity is the presenting symptom in 9% of cases.
• Bowel obstruction: Complete obstruction of the large bowel is rare and is the presenting symptom in 9% of cases.
• Pelvic pain: This late symptom usually indicates nerve trunk involvement and is present in 5% of cases.
• Other presentations include emergencies such as peritonitis from perforation (3%) or jaundice, which may occur with liver metastases ( <1%)

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