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About
Endometrial Cancer
Endometrial cancer
originates in the endometrial lining of the uterus. It is the most common
gynecologic malignancy (cancer originating in female reproductive organs). It is
estimated that there are about 35,000 cases diagnosed each year in the United
States, resulting in 4000 - 5000 deaths per year. The disease normally occurs in
postmenopausal women; the average age at diagnosis of endometrial cancer is about 60 years.
Endometrial cancer is
considered an estrogen-dependent disease. Estrogen is a hormone that is secreted
by the ovaries. Endometrial cancer plays an important role in the development of the female
reproductive system and is largely responsible for the physiologic changes that
occur during menstruation, puberty, and pregnancy. Progesterone is another
hormone secreted by the ovaries that plays an important role in endometrial cancer. Normally, both
estrogen and progesterone are secreted in certain proportions. Chronic exposure
to estrogen, without the accompanying balancing effects of progesterone, is
considered the major risk factor for endometrial cancer and may play a causal
role in the development of the disease.
Benign uterine tumors,
known as fibroids, usually are asymptomatic and do not require treatment. If
fibroids cause bleeding or pain, they may be surgically removed. Cancerous
(malignant) uterine tumors spread to other tissues and organs if left untreated.
Endometrial cancer refers specifically to tumors that originate in the
endometrial lining of the uterus. If the tumor originates in the deeper,
muscular walls of the uterus, it is called uterine sarcoma. About 90% of all
uterine cancers are endometrial.
A precancerous condition
called endometrial hyperplasia, or adenomatous hyperplasiam, may cause irregular
uterine bleeding. This condition can be mild, moderate, or severe. Severe
hyperplasia is considered carcinoma in situ, the earliest detectable stage of
endometrial cancer.
Incidence and
Prevalence
Endometrial cancer is the most common gynecologic cancer and the fourth most
common cancer in women in the United States. Worldwide, it is the fifth most
common cancer in women. It is estimated that there are approximately 35,000 new
cases of endometrial cancer reported annually in the United States, and nearly
5000 deaths. The death rate fell more than 50% from 1950-1970 and has continued
to decline, due in large part to earlier diagnosis and more effective treatment.
Though the incidence of endometrial cancer rose rapidly for a while in the
1970s, presumably due to an increased use of menopausal estrogen therapy (which
has been linked to the disease), it has since stabilized. Endometrial cancer incidence is
increasing, however, in many economically underdeveloped countries.
In the United States, the
incidence rates of endometrial cancer are much higher for Caucasian women than
for African American women, although the incidence rate in Caucasian women has
been declining over the past thirty years. It has remained steady for African
American women. Importantly, however, the incidence-to-mortality ratio (the
number of women who have endometrial cancer and die from the disease) is much
lower, 2:1, for African American women and 7:1 for Caucasian women. Thus even
though a greater percentage of Caucasian women are diagnosed with endometrial
cancer, a smaller percentage of them die from the disease. The ratio of
incidence to mortality for Hawaiian women is 3:1. The smaller
incidence-to-mortality ratios among African American and Hawaiian women suggest
that access to health care may be an issue. It is likely that endometrial cancer
in Caucasian women is diagnosed at an earlier stage and thus easier to be treat
Anatomy of the uterus
and endometrium
The uterus (womb) is a muscular, upside-down, pear-shaped organ that is located
in a woman's pelvis behind the bladder and in front of the rectum. The top,
wider part of the uterus is called the fundus (body), and the bottom, narrow
part is the cervix. The fundus has very thick, muscular walls that are lined
with a mucuous surface called the endometrial.
Two uterine tubes, the
fallopian tubes or oviducts, lead from either side of the upper part of the
uterus to the ovaries. The ovaries are paired organs, one on each side of the
pelvis. Ova (eggs) are transported from the ovaries to the uterus via the
fallopian tubes.
All of the parts of the
female genital tract, from the ovaries to the vagina, are held together by
various types of connective tissue. Thus with endometrial cancer, for example, there is a thin, delicate sheet
of lining called the peritoneum that covers the uterus and extends over the
bladder and rectum, keeping the uterus snug between the latter two organs. But,
despite all the well-connected organs, the female genital tract is more mobile
and plastic than any other part of a woman's body. When there is no endometrial cancer,
the ovaries rupture monthly. The uterus sheds countless cells during menstruation, and the changes that a
woman's uterus undergo during pregnancy are the most dramatic changes that any
human organ experiences without suffering damage. A woman's reproductive system
is incredibly responsive to hormonal changes in its environment. The endometrial
is no exception. It is very sensitive to hormonal changes, and it is believed
that endometrial cancer may be caused by an imbalance in its hormonal
environment.
The endometrial contains
several layers of cells that vary in appearance and amount as a woman's
menstrual cycle changes. It is full of glandular cells and blood vessels. Nearly
all of the cells are responsive to the hormonal changes that the uterus
regularly experiences. Certain cells undergo what is called endometrial
hyperplasia,
increased cell division (cancer?), in response to estrogen. It is this cell-growing
response to estrogen that leads many researchers to believe that estrogen likely
plays a causal role in the development of endometrial cancer.
The uterus has a flat,
inner surface and is covered with tall, columnar epithelial cells. There are
pits in the surface that lead down into uterine glands. The columnar cells, the
pits, and the connective tissue and blood vessels that surround the glands are
all part of the endometrium. The endometriial undergoes dramatic changes during a
woman's menstrual cycle. During the luteal phase, for example, the two-week
period just before a woman bleeds, the endometrial is thick, its epithelial
cells are enlarged, the glands bulging, and the arteries swollen. At
menstruation, the arteries break, the epithelial cells die, and the endometrial,
in effect, sheds. Following menstruation, during the follicular phase, the
endometrial regenerates. The changing thickness of the endometrial is highly
dependent on the secretion of estrogen and progesterone. Estrogen causes
cellular growth and is an important component of the rebuilding, follicular
phase of the menstrual cycle. Progesterone is secreted during the later,
thick-walled luteal phase, and it balances out the effects of the estrogen.
Abnormal growth of endometrial cells (whether cancerous or not) and endometrial
cancer are believed to be due to chronic exposure to too much estrogen without
the balancing effect.
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