Colorectal cancer is the third most commonly diagnosed cancer for both men and women in the United States. Approximately 133,500 new cases will be diagnosed during 1996. For men, colorectal cancer follows prostate and lung cancers in frequency; for women, it follows breast and lung cancers. Approximately 7 percent of Americans are expected to develop colorectal cancer within their lifetimes.
Colorectal cancer is the second leading cause of cancer-related deaths in the United States. In 1996, there will be an estimated 54,900 deaths from colorectal cancer.
Who Is at Risk?
Well-established risk factors for colorectal cancer
are age and male gender. The risk of developing this cancer begins
to increase after the age of 40, rises sharply between the ages
of 50-55, and continues to increase with age. Men are more likely
than women and African Americans are more likely than whites to
be diagnosed with colorectal cancer. Other major risk factors
include inflammatory bowel disease, familial disposition to developing
colon and rectal polyps, and family history of colorectal cancer.
Other conditions contributing to increased risk for colorectal
cancer include a history of colorectal polyps or of ovarian, endometrial,
or breast cancers. Excess dietary fat, alcohol use, sedentary
lifestyle, and obesity are possible risk factors.
Early Detection
Survival is greatly enhanced when colorectal cancer
is treated at an early stage. Survival rates vary significantly
by stage at diagnosis: persons diagnosed at a localized stage
have a 5-year relative survival rate of 91 percent, and those
who are diagnosed at a regional stage have a 5-year survival rate
of 63 percent. For patients diagnosed at an advanced stage of
colorectal cancer (distant metastases), the 5-year survival rate
drops to 7 percent despite advances in surgical technique and
postoperative therapies such as chemotherapy, radiation, and immunotherapy.
Only 37 percent of colorectal cancers are diagnosed while the
disease is still in a localized stage. For African Americans,
the 5-year relative survival rates are lower than those for whites,
and fewer cases are diagnosed at an early stage.
Cancerous polyps and their precursors, benign adenomatous
polyps, may be present in the colon for years before invasive
cancer develops. Reducing the number of deaths from colorectal
cancer depends on detecting and removing precancerous polyps and
detecting and treating invasive cancer in its earliest stages.
Three tests are currently available for colorectal cancer:
Fecal Occult Blood Testing
(FOBT) is a chemical test for blood in a stool sample. A positive
test can indicate bleeding from a precancerous growth or from
colorectal cancer. However, FOBT has the potential for false-positive
and false-negative results. False-positive results can be caused
by other medical conditions or by the use of aspirin and nonsteroidal
anti-inflammatory drugs, which can cause bleeding. Recent consumption
of raw fruit, vegetables, or red meat can also produce false-positive
results. False-negative tests may result because polyps and some
cancers may not cause bleeding or do so only intermittently.
Sigmoidoscopy uses a hollow,
lighted tube to visually inspect the wall of the rectum and distal
colon. The 35-centimeter flexible sigmoidoscope can detect about
50-55 percent of polyps; the longer 60-centimeter flexible scope
is capable of detecting about 65-75 percent of polyps and 40-65
percent of colorectal cancers. The flexible sigmoidoscopes are
now preferred over the rigid sigmoidoscope because they permit
a more complete examination of the colon and provide greater patient
comfort during the procedure.
Digital Rectal Examination
(DRE) is the most commonly used screening test for colorectal
cancer because it can be incorporated easily into routine physical
exams, requires no special equipment, and is commonly performed
to check the prostate in men as well. However, DRE can detect
only those tumors within about 10 centimeters of the anus.
Follow-up diagnostic tests include colonoscopy and
barium enema. These tests allow inspection of the entire colon
and are usually recommended when a screening test is positive.
Guidelines for Screening
Recent studies have provided new evidence that screening
reduces mortality from colorectal cancer. On the basis of a systematic
and rigorous review of these new data, the U.S. Preventive Services
Task Force (USPSTF), an independent, expert advisory panel convened
by the U.S. Public Health Service, has concluded that there is
now sufficient evidence to issue new recommendations on screening.
In the second edition of the Guide to Clinical Preventive Services,
the USPSTF recommends that clinicians include colorectal cancer
screening, with periodic flexible sigmoidoscopy and/or annual
fecal occult blood testing (FOBT), in the periodic health examination
of all persons aged 50 and over. There is insufficient evidence
to determine which of these screening methods is preferable or
whether the combination of FOBT and sigmoidoscopy produces greater
benefits than either test alone. Currently, the American Cancer
Society (ACS) recommends an annual FOBT for those aged 50 and
over, flexible sigmoidoscopy every 3-5 years for those aged 50
and over, and a DRE annually for people aged 40 and over.
The health benefit derived from colorectal cancer
screening is supported by a randomized control trial using FOBT's
that showed a 33 percent reduction in mortality in the group chosen
to undergo annual screening. The efficacy of sigmoidoscopy has
not been tested in a randomized control trial, but is supported
by two case-control studies. The efficacy of DRE in reducing the
number of deaths from colorectal cancer has not been documented.
Results from these studies and the new USPSTF guidelines
highlight the need to increase screening for colorectal cancer
with effective methods such as FOBT and sigmoidoscopy. Screening
for colorectal cancer lags behind screening for breast and cervical
cancers (see graph), perhaps because the effectiveness of screening
has only recently been documented. In the 1992 National Health
Interview Survey, almost 17 percent of persons aged 50 or older
had never heard of an FOBT for screening, and over 32 percent
had never heard of sigmoidoscopy. About 26 percent reported having
had an FOBT for screening in the past 3 years, and only about
9 percent reported having had screening sigmoidoscopy in the past
3 years. These statistics underscore the need for greater effort
to educate health care providers about the new colorectal cancer
screening guidelines and to inform the public, especially the
targeted older population, about the availability and advisability
of screening.
Colorectal Cancer: Average Annual Age-Specific
Incidence and Mortality Rates by Gender, 1987-1991 (Graph)
