InfoTrac
Web: Health Reference Center-Academic.
AL General
AT Rectal cancer.
AU Richard A. MD McCartney
AU Teresa G. Odle
CT Gale Encyclopedia of Medicine
DE Colorectal cancer_Risk factors
DE Colorectal cancer_Diagnosis
DE Colorectal cancer_Care and treatment
DE Colorectal cancer_Prognosis
DP Jan 1, 2004 pNA
LW NA
ND 20050723
PB Thomson Gale
PT Encyclopedia
RM COPYRIGHT 2005 Gale Group
SU Colorectal cancer_Risk factors
SU Colorectal cancer_Diagnosis
SU Colorectal cancer_Care and treatment
SU Colorectal cancer_Prognosis
SU Risk factors
SU Diagnosis
SU Care and treatment
SU Prognosis
XX 4750
ZZ
Source: Gale Encyclopedia
of Medicine, Jan 1, 2004 pNA.
Title: Rectal cancer.
Author: Richard A. MD McCartney and Teresa G. Odle
Subjects: Colorectal cancer - Risk factors
Colorectal cancer -
Diagnosis
Colorectal cancer -
Care and treatment
Colorectal cancer -
Prognosis
Locations:
Electronic Collection: A133987213
RN: A133987213
Full Text COPYRIGHT 2004 Thomson Gale
Definition
The rectum is the portion of the large bowel that lies in the pelvis, terminating
at the anus. Cancer of the rectum is the disease characterized by the
development of malignant cells in the lining or epithelium of the rectum.
Malignant cells have changed such that they lose normal control
mechanisms governing growth. These cells may invade surrounding local tissue or
they may spread throughout the body and invade other organ systems.
Description
The rectum is the continuation of the colon (part of the large bowel)
after it leaves the abdomen and descends into the pelvis. It is divided into
equal
thirds: the upper, mid,
and lower rectum.
The pelvis and other organs in the pelvis form boundaries to the rectum.
Behind, or posterior to the rectum is the sacrum (the lowest portion of
the spine, closest to the pelvis). Laterally, on the sides, the rectum is
bounded by soft tissue and bone. In front, the rectum is bounded by different
organs in the male and female. In the male, the bladder and prostate are
present. In the female, the vagina, uterus, and ovaries are present.
The upper rectum receives its blood supply from branches of the inferior
mesenteric artery from the abdomen. The lower rectum has blood vessels entering
from the sides of the pelvis. Lymph, a protein-rich fluid that bathes the cells
of the body, is transported in small channels known as lymphatics.
These channels run with the blood supply of the rectum. Lymph nodes are
small filters through which the lymph flows on its way back to the blood
stream.
Cancer spreads elsewhere in the body by invading the lymph and vascular
systems.
When a cell or cells lining the rectum become malignant, they first grow
locally and may invade partially or totally through the wall of the rectum.
The tumor here may invade surrounding tissue
or the organs that bound it, a process known as local invasion. In this
process, the tumor penetrates and may invade the lymphatics or the capillaries locally and gain access to
the circulation in this way. As the malignant cells work their way to other
areas of the body, they again become locally invasive in the new area to which
they have spread. These tumor deposits, originating
in the primary tumor in the rectum, are then known as
metastasis. If metastases are found in the regional lymph nodes, they are known
as regional metastases. If they are distant from the primary tumor, they are known as distant metastases. The patient
with distant metastases may have widespread disease, also referred to as
systemic disease. Thus the cancer originating in the rectum begins locally and,
given time, may become systemic.
By the time the primary tumor is originally
detected, it is usually larger than 1 cm (about 0.39 in) in size and has over
one million cells. This amount of growth is estimated to take about three to
seven years. Each time the cells double in number, the size of the tumor quadruples. Thus like most cancers, the part that is
identified clinically is later in the progression than
would be desired. Screening becomes a very important endeavor
to aid in earlier detection of this disease.
Passage of red blood with the stool, (noticeable bleeding with
defecation), is much more common in rectal cancer than that originating in the
colon because the tumor is much closer to the anus.
Other symptoms (constipation and/ or
diarrhea) are caused by obstruction and, less often, by local invasion of the tumor into pelvic organs or the sacrum. When the tumor has spread to distant sites, these metastases may
cause dysfunction of the organ they have spread to. Distant metastasis usually
occurs in the liver, less often to the lung(s), and rarely to the brain.
There are about 36,500 cases of rectal cancer diagnosed per year in the
Cancer of the rectum is felt to arise sporadically in about 80% of those
who develop the disease. About 20% of cases probably arise from genetic
predisposition; some people have a family history of rectal cancer occurring in
a first-degree relative. Development of rectal cancer at an early age suggests
a genetically transmitted form of the disease as opposed to the sporadic form.
Causes and symptoms
Causes of rectal cancer are probably environmental in sporadic cases
(80%), and genetic in the heredity-predisposed (20%) cases. Since malignant
cells have a changed genetic makeup, this means that in 80% of cases, the
environment spontaneously induces change. Those born with a genetic
predisposition are either destined to get the cancer, or it will take less
environmental exposure to induce the cancer. Exposure to agents in the
environment that may induce mutation is the process of carcinogenesis and is
caused by agents known as carcinogens. Specific carcinogens have been difficult
to identify; dietary factors, however, seem to be involved.
Rectal cancer is more common in industrialized nations. Dietary factors
may be the reason. Diets high in fat, red meat, total calories, and alcohol
seem to add to increased risk. Diets high in fiber
are associated with a decreased risk. High-fiber
diets may be related to less exposure of the rectal epithelium to carcinogens
from the environment as the transit time through the bowel is faster with a
high-fiber diet than with a low-fiber
diet.
Age plays a definite role in rectal cancer risk. Rectal cancer is rare
before age 40. This incidence increases substantially after age 50 and doubles
with each succeeding decade.
There also is a slight increase of risk for rectal cancer in the
individual who smokes.
Patients who suffer from an inflammatory disease of the colon known as
ulcerative colitis are also at increased risk.
On chromosome 5 is the APC gene associated with familial adenomatous polyposis
(FAP) syndrome.
There are multiple mutations that occur at this site, yet they all cause a
defect in tumor suppression that
results in early and frequent development of colon cancer. This is
transmitted to 50% of offspring and each of those affected will develop colon
or rectal cancer, usually at an early age. Another syndrome, hereditary non-polyposis colon cancer (HNPCC), is related to mutations in
any of four genes responsible for DNA mismatch repair.
In patients with colon or rectal cancer, the p53 gene is mutated 70% of
the time. When the p53 gene is mutated and ineffective, cells with damaged DNA
escape repair or destruction, allowing the damaged cell to multiply. Continued replication
of the damaged DNA may lead to tumor development.
Though these syndromes (FAP and HNPCC) have a very high incidence of colon or
rectal cancer, family history without the syndromes is also a substantial risk
factor. When considering first-degree relatives, history of one with colon or
rectal cancer raises the baseline risk from 2% to 6%; the presence of a second
raises the risk to 17%.
The development of polyps of the colon or rectum commonly precedes the
development of rectal cancer. Polyps are growths of the rectal lining. They can
be unrelated to cancer, pre-cancerous, or malignant. Polyps, when identified,
are removed for diagnosis. If the polyp, or polyps, are
benign, the patient should undergo careful surveillance for the development of
more polyps or the development of colon or rectal cancer.
Symptoms of rectal cancer most often result from the local presence of
the tumor and its capacity to invade surrounding
pelvic structure:
*bright red blood present with stool
*abdominal distention (stretching from
internal pressure), bloating, inability to have a bowel movement
*narrowing of the stool, so-called ribbon stools
*pelvic pain
*unexplained weight loss
*persistent chronic fatigue
*rarely, urinary infection or passage of air in urine in males (late
symptom)
*rarely, passage of feces through vagina in females(late symptom)
If the tumor is large and obstructing the
rectum, the patient will not be evacuating stool normally and will get bloated
and have abdominal discomfort.
The tumor itself may bleed and, since it is
near the anus, the patient may see bright red blood on the surface of the
stool. Blood alone (without stool) may also be passed. Thus, hemorrhoids are often incorrectly blamed for bleeding,
delaying the diagnosis. If anemia develops, which is
rare, the patient will experience chronic fatigue. If the tumor
invades the bladder in the male or the vagina in the female, stool will get
where it doesn't belong and cause infection or discharge. (This condition is
also rare.) Patients with widespread disease lose weight secondary to the
chronic illness.
Diagnosis
Screening evaluation of the colon and rectum are accomplished together.
Screening involves physical exam, simple laboratory tests, and the
visualization of the lining of the rectum and colon. X rays (indirect
visualization)
and endoscopy (direct visualization) are used to
visualize the organs' lining.
The physical examination involves the performance of a digital rectal
exam (DRE). At the time of this exam, the physician checks the stool on the
examining glove with a chemical to see if any occult (invisible), blood is
present. At home, after having a bowel movement, the patient is asked to swipe
a sample of stool obtained with a small stick on a card. After three such
specimens are on the card, the card is then easily chemically tested for occult
blood. These exams are accomplished as an easy part of a routine yearly
physical exam.
Proteins are sometimes produced by cancers and these may be elevated in
the patients blood. When this occurs
the protein produced is known as a tumor marker.
There is a tumor marker for cancer of the colon and
rectum; it is known as carcinoembryonic antigen,
(CEA). Unfortunately, this may be made by other adenocarcinomas
as well, or it may not be produced by a particular colon or rectal cancer.
Therefore, screening by chemical analysis for CEA has not been helpful. CEA has
been helpful in patients treated for colon or rectal cancer if their tumor makes the protein. It is used in a follow-up role,
not a screening role.
Direct visualization of the lining of the rectum is accomplished using a
scope or endoscope. The physician introduces the instrument into the rectum and
is able to see the epithelium of the rectum directly. A simple rigid tubular
scope may be used to see the rectal epithelium; however, screening of the colon
is done at the same time. The lower colon may be visualized using a fiberoptic flexible scope in a procedure known as flexible sigmoidoscopy. When the entire colon is visualized, the procedure
is known as total colonoscopy.
Each type of endoscopy requires pre-procedure
preparation (evacuation) of the rectum and colon.
The American Cancer Society has recommended the following screening
protocol for colon and rectal cancers those over age 50:
*yearly fecal occult blood test
*flexible sigmoidoscopy at age 50
*flexible sigmoidoscopy repeated every 5 years
*double contrast barium enema every five years
*colonoscopy every 10 years
If there are predisposing factors such as positive family history,
history of polyps, or a familial syndrome, screening evaluations should start
sooner.
Evaluation of patients with symptoms
When patients visit their physician because they are experiencing
symptoms that could possibly be related to colon or rectal cancer, the entire
colon and rectum must be visualized. Even if a rectal lesion is identified, the
entire colon must be screened to rule out a syndromous
polyp or cancer of the colon.
The combination of a flexible sigmoidoscopy
and double contrast barium enema may be performed, but the much preferred
evaluation of the entire colon and rectum is that of complete colonoscopy.
Colonoscopy allows direct visualization, photography, as well as the
opportunity to obtain a biopsy, (a sample of tissue), of any abnormality
visualized. If, for technical reasons the entire colon is not visualized endoscopically, a double contrast barium enema should
complement the colonoscopy. A patient who is identified to have a problem in
one area of the colon or rectum is at greater risk to have a similar problem in
area of the colon or rectum. Therefore the entire colon and rectum need to be
visualized during the evaluation.
The diagnosis of rectal cancer is actually made by the performance of a
biopsy of any abnormal lesion in the rectum. Many rectal cancers are within
reach of the examiner's finger. Identifying how close to the anus the cancer
has developed is very important in planning the treatment. Another
characteristic ascertained by exam is whether the tumor
is mobile or fixed to surrounding structure. Again, this will have implications
related to primary treatment. As a general rule, it is easier to identify and
adequately obtain tissue for evaluation in the rectum as opposed to the colon.
This is because the lesion is closer to the anus.
If the patient has advanced disease, areas where the tumor
has spread, such as the liver, may require biopsy. Such biopsies are usually
obtained using a special needle under local anesthesia.
Once a diagnosis of rectal cancer has been established by biopsy, in
addition to the physical exam, an endorectal
ultrasound will be performed to assess the extent of the disease. For rectal
cancer, endorectal ultrasound is the most preferred
method for staging both depth of tumor penetration
and local lymph node status. Endorectal ultrasound:
*differentiates areas of invasion within large rectal adenomas that seem
benign
*determines the depth of tumor penetration
into the rectal wall
*determines the extent of regional lymph node invasion
*can be combined with other tests (chest x rays and computed tomography
scans, or CT scans) to determine the extent of cancer spread to distant organs,
such as the lungs or liver
The resulting rectal cancer
staging allows physicians to determine the need for--and order of--radiation,
surgery, and chemotherapy. In 2003, it was reported that magnetic resonance
imaging (MRI) also may be useful in staging rectal cancer. MRI may help
physicians determine if a tumor can be resected and risk of cancer recurrence.
Treatment
Once the diagnosis has been confirmed by biopsy and the endorectal ultrasound has been performed, the clinical
stage of the cancer is assigned. The treating physicians use staging to plan
the specific treatment protocol for the patient. In addition, the stage of the
cancer at the time of presentation gives a statistical likelihood of the
treatment outcome (prognosis).
Clinical staging
Rectal cancer first invades locally and then progresses to spread to
regional lymph nodes or to other organs. Stage is derived using the
characteristics of the primary tumor, its depth of
penetration through the rectum, local invasion into pelvic structure, and the
presence or absence of regional or distant metastases.
Rectal cancer is assigned stages I through IV, based on the following
general
criteria:
*Stage I: the tumor is confined to the
epithelium or has not penetrated through the first layer of muscle in the
rectal wall.
*Stage II: the tumor has penetrated through to
the outer wall of the rectum or has gone through it, possibly invading other
local tissue or organs.
*Stage III: Any depth or size of tumor
associated with regional lymph node involvement.
*Stage IV: any of previous criteria associated with distant metastasis.
Surgery
The first, or primary, treatment modality utilized in the treatment of
rectal cancer is surgery. Stage I, II, and even suspected stage III disease are
treated by surgical removal of the involved section of the rectum along with
the complete vascular and lymphatic supply. Most Stage II and Stage III rectal
cancers (based on endorectal ultrasound, CT scan, and
chest x ray) are treated with radiation and possibly
chemotherapy prior to surgery.
When determining primary treatment for rectal cancer, the surgeon's
ability to reconnect the ends of the rectum. The pelvis is a confining space
that makes the performance of the hook-up more difficult to do safely when the tumor is in the lower rectum. The upper rectum does not
usually present a substantial problem to the surgeon restoring bowel continuity
after the cancer has been removed. Mid-rectal tumors,
(especially in males where the pelvis is usually smaller than a woman's), may
present technical difficulties in hooking the proximal bowel to the remaining
rectum. Technical advances in stapling instrumentation have largely overcome
these difficulties. If the anastomosis
(hook-up) leaks postoperatively, infection can occur. In the past, this
was a major cause of complications in resection of rectal cancers. Today,
utilizing the stapling instrumentation, a hook-up at the time of original
surgery is much safer. If the surgeon feels that the hook-up is compromised or
may leak, a colostomy may be performed. A colostomy is performed by bringing
the colon through the abdominal wall and sewing it to the skin. In these cases
the stool is diverted away from the hook-up, allowing it to heal and preventing
the infectious complications associated with leak. Later, when the hook-up has
completely healed, the colostomy can be taken down and bowel continuity
restored.
Stapling devices have allowed the surgeon to get closer to the anus and
still allow the technical performance of a hook-up, but there are limits. It is
generally felt that there should be at least three centimeters
of normal rectum below the tumor or the risk of
recurrence locally will be excessive. In addition, if there is no residual
native rectum, the patient will not have normal sensation or control and will
have problems with uncontrollable soilage,
(incontinence). For these reasons, patients presenting with low rectal tumors may undergo total removal of the rectum and anus.
This procedure is known as an abdominal-perineal
resection. A permanent colostomy is performed in the lower left abdomen.
Radiation
As mentioned, for many late stage II or stage III tumors,
radiation therapy can shrink the tumor prior to
surgery. The other roles for radiation therapy are as an aid to surgical
therapy in locally advanced disease that has been removed, and in the treatment
of certain distant metastases. Especially when utilized in combination with
chemotherapy, radiation used postoperatively has been shown to reduce the risk
of local recurrence in the pelvis by 46% and death rates by 29%. Such combined
therapy is recommended in patients with locally advanced primary tumors that have been removed surgically. Radiation has
been helpful in treating effects of distant metastases, particularly in the
brain. In very few cases, radiation alone may be the curative treatment for
rectal cancer.
Chemotherapy
Adjuvant chemotherapy, (treating the patient who has no evidence of
residual disease but who is at high risk for recurrence), is considered in
patients whose tumors deeply penetrate or locally
invade (late stage II and stage III).
If the tumor was not locally advanced, this
form of chemotherapeutic adjuvant therapy may be recommended without radiation.
This therapy is identical to that of colon cancer and leads to similar results.
Standard therapy is treatment with 5-fluorouracil, (5-FU) combined with leucovorin for a period of six to 12 months. 5-FU is an antimetabolite and leucovorin
improves the response rate. Another agent, levamisole,
(which seems to stimulate the immune system), may be substituted for leucovorin. These protocols reduce rate of recurrence by
about 15% and reduce mortality by about 10%. The regimens have some toxicity
but usually are tolerated fairly well.
Similar chemotherapy is administered for stage IV disease or if a cancer
progresses and metastasis develops. Results show response rates of about 20%.
A response is a temporary regression of the cancer in response to the
chemotherapy. Unfortunately, these patients eventually succumb to the disease.
Clinical trials have now shown that the results can be improved with the
addition of another agent to this regimen. Irinotecan
does not seem to increase toxicity but has improved response rates to 39%,
added two to three months to disease free survival, and prolonged overall
survival by a little more than two months.
Alternative treatment
Most alternative therapies have not been studied in clinical trials.
Large doses of vitamins, fiber, and green tea are
among therapies tried. A 2003 report on a large
Prognosis
Prognosis is the long-term outlook or survival after therapy. Overall,
about 50% of patients treated for colon and rectal cancer survive the disease.
As expected, the survival rates are dependent upon the stage of the cancer at
the time of diagnosis, making early detection crucial.
About 15% of patients present with stage I disease, or are diagnosed
with Stage I disease when they initially visit a doctor, and 85-90% survive.
Stage II represents 20-30% of cases and 65-75% survive;
30-40% comprise the stage III presentation, of which 55% survive. The remaining
20-25% present with stage IV disease and are rarely cured.
Prevention
There is not an absolute method for preventing colon or rectal cancer.
An individual can lessen risk or identify the precursors of colon and rectal
cancer. The patient with a familial history can enter screening and
surveillance programs earlier than the general population. High-fiber diets and vitamins, avoiding obesity, and staying
active lessen the risk. In fact, a
2003 report said that vigorous exercise (to the point of sweating or
feeling out of breath) lowered risk of rectal cancer by nearly 40% compared to
those who exercised less. Avoiding cigarettes and alcohol may be helpful. By
controlling these environmental factors, an individual can lessen risk and to
this degree prevent the disease.
By undergoing appropriate screening when uncontrollable genetic risk
factors have been identified, an individual may be rewarded by the
identification of benign polyps that can be treated as opposed to having these
growths degenerate into a malignancy.
An endoscopic view of a
rectal tumor.
(Custom Medical Stock Photo. Reproduced by permission.)
For More Information
Books
Abelhoff,
Niederhuber
MD. Clinical Oncology Library.
Jorde, Lynn B., PhD, John C. Carey
MD, Michael J. Bamshad MD, and Raymond L.
White, PhD. Medical Genetics,
Second Edition.
Third Edition.
Periodicals
Greenlee, Robert T., PhD, MPH,
Mary Beth Hill-Harmon, MSPH, Taylor Murray, and Michael Thun,
MD, MS. "Cancer Statistics 2001." CA: A Cancer Journal for
Clinicians,
51, no. 1 (Jan/Feb 2001).
Saltz,
Leonard, et al. "Irinotecan plus Fluorouracil
and Leucovorin for Metastatic
Colorectal Cancer." The
343, no. 13 (September 28, 2000).
Periodicals
"
(Dec. 15, 2003).
"Endoscopy
and MRI Are Important in Staging Rectal Cancer." Clinical Oncology Week
(October 6, 2003):56.
Splete,
Heidi. "Multivitamins May Lower Risk of Rectal Cancer: Drops 34% at
15 Years." Family Practice News
(December 1, 2003):33.
"Vigourous
Physical Activity May Reduce the Risk of Rectal Cancer."
Environmental Nutrition
(October 2003):8.
Organizations
American Cancer
Society.
(800)ACS-2345. http://www.cancer.org.
Cancer
Information Service of the NCI. 9000 Rockville Pike,
Building 31,
Other
National Cancer Institute Clinical Trials.
http://www.cancertrials.nci.nih.gov.
Key Terms
Adenocarcinoma
Type of cancer beginning in glandular epithelium.
Adjuvant therapy
Treatment involving radiation, chemotherapy (drug
treatment), or hormone therapy, or a combination of all three given after the
primary treatment for the possibility of residual microscopic disease.
Anastomosis
Surgical re-connection of the ends of the bowel after
removal of a portion of the bowel.
Anemia
The condition caused by too few circulating red blood cells, often
manifest in part by fatigue.
Carcinogens
Substances in the environment that cause cancer,
presumably by inducing mutations, with prolonged exposure.
Defecation
The act of having a bowel movement.
Epithelium
Cells composing the lining of an organ.
Lymphatics
Channels that are conduits for lymph.
Lymph nodes
Cellular filters through which lymphatics
flow.
Malignant
Cells that have been altered such that they have lost normal control
mechanisms and are capable of local invasion and spread to other areas of the
body.
Metastasis
Site of invasive tumor
growth that originated from a malignancy elsewhere in the body.
Mutation
A change in the genetic makeup of a cell that may
occur spontaneously or be environmentally induced.
Occult blood
Presence of blood that cannot be appreciated visually.
Polyps
Localized growths of the epithelium that can be
benign, pre-cancerous, or harbor malignancy.
Resect
To remove surgically.
Sacrum
Posterior bony wall of the pelvis.
Systemic
Referring to throughout the body.
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