by David A. Garcia, MD
Having recently participated in a colorectal
cancer screening lecture, I was impressed by
the number of questions from the public as
well as medical providers with regard to the risk factors
for colorectal cancer and current recommendations
for colorectal cancer screening.
Incidence
Colorectal cancer is the second leading cause of
cancer death after lung cancer in the United States.
About 148,000 new cases are diagnosed each year,
and 58,000 Americans die annually. Among the
general population, the lifetime risk of cancer is 5
percent to 6 percent, but age-adjusted mortality is
higher among men.
Risk Factors
Average Risk Patient
• Age older than 50 years
• No personal history or family history of
colon cancer
• No personal history or family history of
colon polyps
Recommendations
Screening interval is indicated by findings on
the initial screening test such as occult blood,
abnormal DNA in stool, polyps, colorectal cancer,
and family history.
Fecal Occult Blood Testing (FOBT): This test is
inexpensive, convenient, and non-invasive in that it
does not require special equipment other than an
occult blood testing card. It can be performed at
home and mailed to a laboratory. FOBT has a high
sensitivity for heme (blood), but it has a low specificity
for colon cancer. This test is recommended
yearly. If occult blood is detected, the further gastrointestinal
evaluation is recommended.
Flexible Sigmoidoscopy (FS): This test is invasive
and is routinely preformed without sedation. FS surveys
only the left colon. Historically, 29 percent of
left-sided colon polyps smaller than one centimeter
(cm) have been associated with right-sided colon
lesions, while 75 percent of left-sided colon polyps
greater than one cm have been associated with more
advanced right-sided colon lesions. This exam is recommended
every five years. Colonoscopy is recommended
if polyps or lesions are found.
Air Contrast Barium Enema (ACBE): This test is
invasive in that an enema is inserted into the rectum.
The colon is then insufflated with air and barium is
infused into the colon. ACBE is routinely performed
without sedation. This exam does expose the patient
to radiation. Although this radiation exposure is initially
a small amount, it is likely to increase with
repeated screenings. A cathartic is required to cleanse
the colon of debris such as stool that can be misinterpreted
as polyps or lesions. Unfortunately, as many as
50 percent of colonic polyps and lesions one cm or
smaller can be missed. This exam is recommended
every 10 years. Colonoscopy is recommended if
polyps or lesions are detected.
CT Colonography (CTC): This test is invasive in that an enema is inserted into the rectum. The
colon is then insufflated with air. CTC is routinely
performed without sedation. This exam does expose
the patient to radiation. Although, this radiation
exposure is a small amount, it is likely to increase
with repeated screenings. A cathartic is required to
cleanse the colon of debris such as stool that can be
misinterpreted as polyps or lesions. Unfortunately,
polyps less than one cm may not be detected. CTC
is recommended every 10 years. Colonoscopy is
recommended if polyps or lesions are detected.
Fecal DNA Testing (FDT): This is a non-invasive test.
FDT is more expensive that FOBT. FDT may be performed
at home. This test detects up to 52 percent of
colon cancers and 15 percent of large polyps. FDT is
recommended every five years if negative. Colonoscopy
is recommended if abnormal DNA is detected.
Capsule Colonoscopy: This exam is not currently
available. It will be minimally invasive, although
it will be expensive. Detected polyps cannot be
removed. There is the possibility of intestinal obstruction
by the capsule when strictures are encountered.
Colonoscopy is recommended for abnormal exams.
Colonoscopy: This exam is invasive. Sedation is
routinely used. Time off from work is required due
to sedation. Colonoscopy is operator dependant, as
are the other exams mentioned above. In experienced
hands, colonoscopy has a sensitivity and
specificity of 95 percent to 98 percent. Colonoscopy
surveys the entire colon and terminal ileum. A
colon prep is required to cleanse the colon of any
debris. Polyps can be removed and lesions can be
biopsied. Colonoscopy is recommended every 10
years for average risk patients, and every three years
for high risk patients. Colonoscopy is covered by
Medicare and most insurance.
Patients at high risk for colorectal cancer include:
1) Family history of colorectal cancer or adenomatous
colon polypsis in first degree relative
younger than 50. Screening colonoscopy interval
is every one to three years as indicated by findings
on the initial colonoscopy such as polyps
or colorectal cancer.
2) Personal history of colorectal cancer or adenomatous
polypsis. Patients with adenomas larger
than one cm, flat adenomas, or more than three
ademonatous polyps should have screening
colonoscopy every one to three years.
3) Familial Adenomatous Polyposis Syndrome
(FAP). Patients with a first degree relative with
FAP should have gene testing for APC (Adenomatous
Polyposis Coli) gene at 10 years to 12
years old. Patients with the confirmed APC
(Adenomatous Polyposis Coli) gene should begin
yearly screening sigmoidoscopy at 12 years old. If
polypsis is present at the initial screening examination,
then colectomy should be considered due
to inevitable colorectal cancer by 39 years old. If
examinations are negative for polyposis, then the
screening interval decreases with each subsequent
decade. Patients are considered average risk at age
50 if polyposis is consistently absent.
4) Hereditary None Polyposis Colorectal Cancer
(HNPCC). Patients with HNPCC have a 70 percent
to 80 percent lifetime risk of developing
colorectal cancer. Patients with HNPCC are
characterized by having:
• Three or more relatives with histologically
verified colorectal cancer; one of whom is a
first degree relative of the other two;
• Colorectal cancer involving at least
two generations;
• One or more colorectal cancer cases diagnosed
before age 50; and
• Extracolonic cancers including endometrium,
upper GI tract, and urinary tract.
Screening colonoscopy is offered every one to
two years starting at age 20 to 25, or 10 years earlier
than the youngest age of colorectal cancer in
a primary relative.
5) Inflammatory Bowel Disease (Crohn’s Disease
and Ulcerative Colitis). Screening colonoscopy is
offered every one to two years with four quadrant
biopsies every 10 cm to rule out dysplasia in
patients with more than eight years of disease
with pancolitis and more than 15 years of disease
in left-sided colitis.
Conclusion
Screening for colorectal cancer is an invaluable
tool, and its use is imperative since approximately 93
percent of cases of colorectal cancer are diagnosed
over age 50, and approximately 80 percent of colorectal
cancer patients have sporadic disease with no evidence
of an inherited disorder. Thirty-nine percent of
colorectal cancers found during a colonoscopy are at
an advanced stage. Screening colonoscopy with clearance
of polyps results in a 70 percent to 90 percent
reduction of colorectal cancer.
David A. Garcia, MD is a gastroenterologist
in solo practice in the
Stone Oak area. Dr. Garcia is Chief
of Internal Medicine at North
Central Baptist Hospital. After completing
training at Scott & White in
Temple, Texas, Dr. Garcia received
board certification in Gastroenterology
and Internal Medicine.
