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BACKGROUND:
Anatomy:
The rectum is the
lowest portion of the large intestine. It begins in the upper
pelvis and ends at the anus. The rectum is approximately
5 inches long and lies within the muscular and fatty tissue
of the pelvis. The blood supply of the upper two thirds of
the rectum drains into the liver. This is why the liver is
often the first site of spread of rectal cancer. There are
lymph nodes immediately surrounding the rectum that drain
into lymph nodes higher in the abdomen.
The wall of the
rectum is made of muscle that is tubular in shape. This tube
is lined by a mucosa, which is where cancers generally arise.
Epidemiology:
There is increasing
evidence that diet plays a role in the development of rectal
cancer. In countries where red meat is popular, there is
a high incidence of colon and rectal cancer. Conversely,
in countries where a diet of starchy food with fiber is the
norm, the incidence of these cancers is low.
There are other
causes. Some cases of colon and rectal cancer are related
to hereditary factors. Still others are related to inflammatory
diseases of the colon such as ulcerative colitis.
STAGING:
Stage A cancer
of the rectum is confined to the inner lining mucosa. Stage
B disease is subgrouped into Stage B1, B2, or B3. B1 means
that the cancer has just started to invade the muscle, but
is not all the way through it. Stage B2 means that the cancer
has gone all the way through the muscle and is into the fatty
tissue surrounding the rectum. Stage B3 disease means that
a cancer has spread into adjacent pelvic organs. Stage C
disease means that lymph nodes are involved. Stage D disease
means that the cancer has spread to another part of the body,
most likely the liver.
TREATMENT
OPTIONS:
Surgery:
Surgery is the
mainstay of rectal cancer treatment. Two different types
of surgery are commonly used. For cancers that are located
in the very lowest part of the rectum, the bottom two inches,
the best option is usually an abdominal perineal resection.
This operation means removal of the rectum and anus. The
patient is left with a colostomy (bag on the abdominal wall)
for evacuation of stool. The other operation, a low anterior
resection, is done for tumors located higher in the rectum.
This surgery removes the upper portion of the rectum while
leaving the lower portion intact. The colon above the area
affected by the disease is then brought down into the pelvis
and attached (anastomosed) to the lower portion of the rectum.
These patients can have normal bowel movements after the surgery.
Radiation:
Radiation therapy
is given after surgery for tumors that have extended through
the wall of the rectum (stage B2 and B3) as well as for cancers
that involve lymph nodes (stage C). The purpose of the radiation
is to eradicate any subclinical micrometastases that may be
in the pelvis after surgery. This means that on occasion
a few cancer cells can remain in the pelvis after the surgery
in spite of the surgeon’s best efforts. These micrometastases
can be too small to detect by any current x-rays or blood
tests. Postoperative radiation therapy can eliminate these
cells and improve the cure rate.
Chemotherapy:
Chemotherapy can
also be given after the surgery as a way of decreasing the
likelihood that the patient will develop recurrent disease
in the pelvis and elsewhere in the body. Typical chemotherapy
drugs include 5-FU and Leucovorin. These medicines are injected
intravenously and are designed to eliminate micrometastatic
cancer throughout the body.
RADIATION
THERAPY:
Radiation therapy
is given to the pelvis five days a week for a total of approximately
five weeks (25 treatments total). The radiation is given
through fields designed to cover all areas of possible spread.
Just a little radiation is given each day, and the dose gradually
builds up enough to have a high chance of controlling any
micrometastatic cancer.
In most patients
the radiation is given after the surgery (postoperative radiation).
In some patients, however, it is necessary to shrink the cancer
before it is removed. In these cases the radiation is given
prior to the surgery (preoperative radiation). The dose and
treatment fields for this preoperative radiation are the same
as for postoperative treatment.
Side-effects:
Radiation therapy
to the pelvis can irritate the pelvic organs. Patients may
notice some abdominal cramping or diarrhea during the radiation, as
well as some irritation of the bladder. These side effects
typically develop after the second week of radiation. Medicines
are available to help ease these side effects.
Sometimes it is
necessary to extend the radiation fields over the lower portion
of the pelvis so that the skin of the perineum is irradiated.
This is necessary in patients who have had abdominal perineal
resections. When the radiation field covers the perineal skin
a significant skin reaction often occurs, comparable to a
moderately severe sunburn. Patients often find this skin
reaction is a major but temporary problem. Creams are available
to help with the skin reaction, but often the difficulties
do not resolve until two weeks after the radiation ends.
Diet:
During the course
of radiation therapy patients are encouraged to stay on a
normal, nutritious diet. A few adjustments in diet, however,
can be helpful in ameliorating side effects. Specifically,
eliminating spicy and fatty foods may be helpful. Also, sometimes
a limitation on dairy products can lessen the diarrhea.
Fiber is certainly
important in maintaining normal bowel movements and preventing
colon cancer, but the intake of fiber during the course of
radiation should be limited. Once the radiation is finished
a diet rich in fiber is advisable.
Further details
on diet can be found in the Nutritionist section of this website.
Peter H. Blitzer, MD, FACR, FACRO
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