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Hormones and Breast Cancer
The hormone estrogen plays a role in the development of sexual traits and in
the functioning of our reproductive systems. The amount of estrogen circulating
in the blood at any given time depends on our age and on lifestyle factors like
body weight and amount of exercise.
Exposure to estrogen over a lifetime is known to influence breast cancer risk.
Women who start menstruating young, go through menopause late, or never
have children have a longer period of exposure to estrogen and a slightly
increased risk for breast cancer. Women who take hormones for an extended
period to relieve menopausal symptoms also have a slightly elevated breast
cancer risk. The effect of birth control pills is uncertain, but they are believed to
raise risk slightly during the time they are being taken.
Lifestyle can make a difference in the amount of estrogen we are ultimately
exposed to. Estrogen levels are known to be elevated in obese women and
may account for their increased risk for breast cancer as well as for recurrence.
Alcohol consumption is also thought to increase estrogen, while exercise is
believed to lower it.
Hormone Replacement Therapy
As we age, less estrogen is produced, and the fluctuations in hormone levels
lead to the hot flashes and sleeplessness some women experience as they go
through menopause. There is great variation in the degree to which women
have any of these symptoms, and many will have no symptoms at all.
For decades, women were encouraged by their doctors to use medication to
replenish their estrogen whether or not they needed relief from menopause
symptoms. There were hopes that it would lower our risk for heart disease and
stroke and -- best of all -- help preserve our youthful appearance.
It was understood that hormone replacement therapy increased breast cancer
risk slightly, but the medical community viewed that as a small price to pay for
improved cardiovascular health -- and eternal youth. That view changed
abruptly in 2002, when the Women's Health Initiative study showed that
hormones slightly increase a woman's risk of heart disease and stroke instead
of lowering it.
Millions of women abandoned hormone replacement therapy after the results of
the study were released, and the following year the incidence of breast cancer
dropped by 6.7%. Other factors may have contributed to this reduction of
14,000 cases of breast cancer per year, but scientists believe that women
stopping hormone therapy was the major factor.
It is now recommended that hormones be taken at a low dose for the shortest
amount of time possible only when needed to relieve troublesome menopausal
symptoms.
Oral Contraceptives
Studies are unclear as to the effects of birth control pills on breast cancer risk.
It does appear that oral contraceptives may slightly raise breast cancer risk in
current or recent users. This increase appears to reverse with time.
Diethylstylbesterol (DES)
DES is a synthetic estrogen that was used by some women during pregnancy
from around 1940 to 1970 to prevent miscarriage and early delivery. It
increases the risk of breast cancer slightly in women who used it and possibly in
their daughters.
Hormone-Like Chemicals in the Environment
In addition to the estrogen we normally produce and the estrogen in pills,
substances in the environment that have a similar chemical structure are
suspected of playing some role in increasing breast cancer risk. These so-called
endocrine disruptors can mimic hormones and act like them in the body, but
little is known about their potential effects. More research is needed to
determine how they might increase breast cancer risk because we are regularly
exposed to them in everyday products like cosmetics, shampoos, plastics,
pesticides, and weed killers.
the functioning of our reproductive systems. The amount of estrogen circulating
in the blood at any given time depends on our age and on lifestyle factors like
body weight and amount of exercise.
Exposure to estrogen over a lifetime is known to influence breast cancer risk.
Women who start menstruating young, go through menopause late, or never
have children have a longer period of exposure to estrogen and a slightly
increased risk for breast cancer. Women who take hormones for an extended
period to relieve menopausal symptoms also have a slightly elevated breast
cancer risk. The effect of birth control pills is uncertain, but they are believed to
raise risk slightly during the time they are being taken.
Lifestyle can make a difference in the amount of estrogen we are ultimately
exposed to. Estrogen levels are known to be elevated in obese women and
may account for their increased risk for breast cancer as well as for recurrence.
Alcohol consumption is also thought to increase estrogen, while exercise is
believed to lower it.
Hormone Replacement Therapy
As we age, less estrogen is produced, and the fluctuations in hormone levels
lead to the hot flashes and sleeplessness some women experience as they go
through menopause. There is great variation in the degree to which women
have any of these symptoms, and many will have no symptoms at all.
For decades, women were encouraged by their doctors to use medication to
replenish their estrogen whether or not they needed relief from menopause
symptoms. There were hopes that it would lower our risk for heart disease and
stroke and -- best of all -- help preserve our youthful appearance.
It was understood that hormone replacement therapy increased breast cancer
risk slightly, but the medical community viewed that as a small price to pay for
improved cardiovascular health -- and eternal youth. That view changed
abruptly in 2002, when the Women's Health Initiative study showed that
hormones slightly increase a woman's risk of heart disease and stroke instead
of lowering it.
Millions of women abandoned hormone replacement therapy after the results of
the study were released, and the following year the incidence of breast cancer
dropped by 6.7%. Other factors may have contributed to this reduction of
14,000 cases of breast cancer per year, but scientists believe that women
stopping hormone therapy was the major factor.
It is now recommended that hormones be taken at a low dose for the shortest
amount of time possible only when needed to relieve troublesome menopausal
symptoms.
Oral Contraceptives
Studies are unclear as to the effects of birth control pills on breast cancer risk.
It does appear that oral contraceptives may slightly raise breast cancer risk in
current or recent users. This increase appears to reverse with time.
Diethylstylbesterol (DES)
DES is a synthetic estrogen that was used by some women during pregnancy
from around 1940 to 1970 to prevent miscarriage and early delivery. It
increases the risk of breast cancer slightly in women who used it and possibly in
their daughters.
Hormone-Like Chemicals in the Environment
In addition to the estrogen we normally produce and the estrogen in pills,
substances in the environment that have a similar chemical structure are
suspected of playing some role in increasing breast cancer risk. These so-called
endocrine disruptors can mimic hormones and act like them in the body, but
little is known about their potential effects. More research is needed to
determine how they might increase breast cancer risk because we are regularly
exposed to them in everyday products like cosmetics, shampoos, plastics,
pesticides, and weed killers.
More Information:
American Cancer Society www.cancer.org
The Decrease in Breast-Cancer Incidence in 2003 in the United States
PM Ravdin, KA Cronin, N Howlader, CD Berg, RT Chlebowski, EJ Feuer, BK Edwards, DA Berry
The New England Journal of Medicine; April 19, 2007
National Cancer Institute www.cancer.gov
Fact Sheet on Oral Contraceptives and Cancer Use
Environmental Risks and Breast Cancer Vassar ERBC Project
American Cancer Society www.cancer.org
The Decrease in Breast-Cancer Incidence in 2003 in the United States
PM Ravdin, KA Cronin, N Howlader, CD Berg, RT Chlebowski, EJ Feuer, BK Edwards, DA Berry
The New England Journal of Medicine; April 19, 2007
National Cancer Institute www.cancer.gov
Fact Sheet on Oral Contraceptives and Cancer Use
Environmental Risks and Breast Cancer Vassar ERBC Project
