Causes, Natural History & Diagnosis of Prostate Cancer
Prostate cancer is the third-leading cause of cancer deaths among men in
the United States. Yet, when detected in its early stages, prostate cancer can
be effectively treated and cured.
What is the prostate?
The prostate gland is a small, walnut-sized gland in men. It is located below
the bladder and surrounds the upper portion of the urethra. The prostate
gland lies in front of the rectum, and its posterior surface can be felt during a
rectal examination. The function of the prostate is to secrete a fluid that
makes up part of the semen.
What is prostate cancer?
It is the most common non-skin cancer in men affecting approximately
234,000 American men each year with approximately 27,000 of these men
dying each year. Prostate cancer is different from most cancers in that an
appreciable percentage of men, particularly older men with a shorter life
expectancy, may have a silent form of this cancer—it will not cause
symptoms or progress beyond the prostate gland during their lifetime.
Sometimes this cancer can be small, slow growing and present limited risk
to the patient. Clinically important prostate cancers can be defined as those
that threaten the well-being or life span of a man.
What are the causes and risks associated with prostate cancer?
Predominately a disease of elderly men, the diagnosis of prostate cancer is
rare before age 40 but increases dramatically thereafter. In the United
States, it is estimated that one in 55 men between the ages of 40 and 59 will
be diagnosed with prostate cancer. This incidence climbs almost to one in
six for men between ages 60 and 79. This association is also reflected in
mortality as prostate cancer accounts for about 10 percent of cancer-related
deaths in men between the ages of 60 and 79 and nearly 25 percent in
those over the age of 80.
There are also ethnic determinants of risk. Blacks are in the highest risk
group, with an
incidence of more than 200 cases per 100,000 black men. The incidence in
Caucasian and Asian men is slightly more than half that of blacks. In
addition, blacks tend to present with more advanced disease and have
poorer overall prognosis than Caucasian or Asian men.
Men with a family history of prostate cancer are at an increased risk of
developing the disease. The risk correlates with the number of first-degree
relatives (father, brother or uncle) affected by prostate cancer and the age at
onset. Men with a family history of disease may have a risk of developing
prostate cancer 2 to 11 times greater than men without a family history of
There is also considerable evidence showing that prostate cancer is more
common in men with a high intake of fat in their diets. The worldwide
difference in prostate cancer incidence may be associated with dietary
intake of soy proteins. In Asian countries such as Japan and the Republic of
Korea where prostate cancer incidence and mortality are just a fraction of
that in North America, soy consumption in the form of tofu, soymilk and miso
is up to 90 times higher than that consumed in the United States. In a study
of more than 40 nations, researchers found soy, on a per calorie basis, to be
the most protective dietary factor. This protective role may be associated with
two of soy's components, genistein and daidzein that may act as weak
estrogens or through other mechanisms. Estrogens are female hormones
that inhibit prostate cancer growth. Some experts have suggested that the
worldwide differences in prostate cancer incidence may also be explained
by the high intake of green tea by residents of Asia.
The intake of other certain dietary factors may also reduce the risk of
developing prostate cancer. Such substances include lycopene and
selenium. Cooked tomatoes are rich sources of lycopene. Lycopenes are
antioxidants that may protect cells from becoming cancerous. Several
studies have shown that the likelihood of developing prostate cancer is
reduced by high intake of lycopene. Researchers found that men ingesting
two or more servings of tomato sauce per week had a 36 percent reduction
in cancer risk compared to those who did not. Selenium intake has also
been reported to lower prostate cancer risk. In a clinical trial designed to
determine if selenium could lower skin cancer recurrences, men who took
selenium had a 63 percent reduction in prostate cancer incidence compared
to those who took a sugar pill (placebo). Attention has also focused on
vitamin D's effect on the prostate. Epidemiologic evidence shows an inverse
relationship between prostate cancer risk and ultraviolet radiation, the
primary source for vitamin D production. This observation has led some to
suggest that higher rates of prostate cancer in the elderly may be partly due
to decreased sun exposure or a decline in the body's ability to make vitamin
D with aging.
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