What are the risk factors for breast cancer?
A risk factor is anything that
affects your chance of getting a disease, such as cancer. Different cancers
have different risk factors. For example, exposing skin to strong sunlight is a
risk factor for skin cancer. Smoking is a risk factor for cancers of the lung,
mouth, larynx (voice box), bladder, kidney, and several other organs.
But risk factors don't tell us
everything. Having a risk factor, or even several, does not mean that you will
get the disease. Most women who have one or more breast cancer risk factors
never develop the disease, while many women with breast cancer have no apparent
risk factors (other than being a woman and growing older). Even when a woman
with risk factors develops breast cancer, it is hard to know just how much
these factors might have contributed.
There are different kinds of
risk factors. Some factors, like a person's age or race, can't be changed.
Others are linked to cancer-causing factors in the environment. Still others
are related personal behaviors, such as smoking, drinking, and diet. Some
factors influence risk more than others, and your risk for breast cancer can
change over time, due to factors such as aging or lifestyle.
Simply being a woman is the main
risk factor for developing breast cancer. Men can develop breast cancer, but
this disease is about 100 times more common among women than men. This is
likely because men have less of the female hormones estrogen and progesterone,
which can promote breast cancer cell growth.
Your risk of developing breast
cancer increases as you get older. About 1 out of 8 invasive breast cancers are
found in women younger than 45, while about 2 of 3 invasive breast cancers are
found in women age 55 or older.
About 5% to 10% of breast cancer
cases are thought to be hereditary, resulting directly from gene defects
(called mutations) inherited from a parent.
BRCA1 and BRCA2: The most common cause of
hereditary breast cancer is an inherited mutation in the BRCA1 and BRCA2 genes.
In normal cells, these genes help prevent cancer by making proteins that keep
the cells from growing abnormally. If you have inherited a mutated copy of
either gene from a parent, you have a high risk of developing breast cancer
during your lifetime.
The risk may be as high as 80%
for members of some families with BRCA mutations. These
cancers tend to occur in younger women and more often affect both breasts than
cancers in women who are not born with one of these gene mutations. Women with
these inherited mutations also have an increased risk for developing other
cancers, particularly ovarian cancer.
In the United States BRCA mutations
are more common in Jewish women of Ashkenazi (Eastern Europe) origin than in
other racial and ethnic groups, but they can occur in any racial or ethnic
group.
Changes in other genes: Other gene mutations can also lead to inherited breast cancers.
These gene mutations are much rarer and often do not increase the risk of
breast cancer as much as the BRCA genes. They are not frequent causes of
inherited breast cancer.
1) ATM: The ATM gene normally helps repair damaged DNA.
Inheriting 2 abnormal copies of this gene causes the disease
ataxia-telangiectasia. Inheriting 1 mutated copy of this gene has been
linked to a high rate of breast cancer in some families.
2) TP53: The TP53 gene gives instructions for making a protein
called p53 that helps stop the growth of abnormal cells. Inherited mutations of
this gene cause Li-Fraumeni syndrome (named
after the 2 researchers who first described it). People with this syndrome have
an increased risk of developing breast cancer, as well as several other
cancers such as leukemia, brain tumors, and sarcomas (cancer of bones or
connective tissue). This is a rare cause of breast cancer.
3) CHEK2: The Li-Fraumeni syndrome can also be caused by inherited mutations in
the CHEK2 gene. Even when it does not cause this syndrome,
it can
increase breast cancer risk about twofold when it is mutated.
4) PTEN: The PTEN gene normally helps regulate cell growth.
Inherited mutations in this gene can cause Cowden syndrome, a rare
disorder in which people are at increased risk for both benign and
malignant breast tumors, as well as growths in the digestive tract, thyroid,
uterus, and ovaries. Defects in this gene can also cause a different syndrome called
Bannayan-Riley-Ruvalcaba syndrome that is not thought to be linked to breast
cancer risk.
5) CDH1: Inherited mutations in this gene cause hereditary diffuse
gastric cancer, a syndrome in which people develop a rare type of stomach
cancer at an early age. Women with mutations in this gene also have an
increased risk of invasive lobular breast cancer.
6) STK11: Defects in this gene can lead to Peutz-Jeghers syndrome.
People with this disorder develop pigmented spots on their lips and in
their mouths, polyps in the urinary and gastrointestinal tracts, and have an
increased risk of many types of cancer, including breast cancer.
Genetic testing: Genetic tests can be done to look for mutations in the BRCA1 and BRCA2 genes
(or some other genes linked to breast cancer risk). Although testing may be
helpful in some situations, the pros and cons need to be considered carefully.
Family history of breast cancer
Breast cancer risk is higher
among women whose close blood relatives have this disease.
Having one first-degree relative
(mother, sister, or daughter) with breast cancer approximately doubles a
woman's risk. Having 2 first-degree relatives increases her risk about 3-fold.
The exact risk is not known, but
women with a family history of breast cancer in a father or brother also have
an increased risk of breast cancer. Altogether, less than 15% of women with
breast cancer have a family member with this disease. This means that most
(over 85%) women who get breast cancer do not have a family
history of this disease.
A woman with cancer in one
breast has a 3- to 4-fold increased risk of developing a new cancer in the
other breast or in another part of the same breast. This is different from a
recurrence (return) of the first cancer.
Overall, white women are
slightly more likely to develop breast cancer than are African-American women,
but African-American women are more likely to die of this cancer. However, in
women under 45 years of age, breast cancer is more common in African- American
women. Asian, Hispanic, and Native-American women have a lower risk of
developing and dying from breast cancer.
Women with denser breast tissue
(as seen on a mammogram) have more glandular tissue and less fatty tissue, and
have a higher risk of breast cancer. Unfortunately, dense breast tissue can
also make it harder for doctors to spot problems on mammograms.
Women diagnosed with certain
benign breast conditions might have an increased risk of breast cancer. Some of
these conditions are more closely linked to breast cancer risk than others.
Doctors often divide benign breast conditions into 3 general groups, depending
on how they affect this risk.
Non-proliferative lesions: These conditions are not associated with overgrowth of breast tissue.
They do not seem to affect breast cancer risk, or if they do, it is to a very
small extent. They include:
1) Fibrosis
and/or simple cysts (this used to be called fibrocystic disease or changes)
2) Mild
hyperplasia
3) Adenosis
(non-sclerosing)
4) Ductal
ectasia
5) Phyllodes
tumor (benign)
6) A
single papilloma
7) Fat
necrosis
8) Periductal
fibrosis
9) Squamous
and apocrine metaplasia
10) Epithelial-related
calcifications
11) Mastitis
(infection of the breast)
12) Other
benign tumors (lipoma, hamartoma, hemangioma, neurofibroma, adenomyoepthelioma)
Proliferative lesions without
atypia: These conditions show excessive growth of
cells in the ducts or lobules of the breast tissue. They seem to raise a
woman's risk of breast cancer slightly (1½ to 2 times normal). They include:
1) Usual
ductal hyperplasia (without atypia)
2) Fibroadenoma
3) Sclerosing
adenosis
4) Several
papillomas (called papillomatosis)
5) Radial
scar
Proliferative lesions with
atypia: In these conditions, there is an overgrowth
of cells in the ducts or lobules of the breast tissue, with some of the cells
no longer appearing normal. They have a stronger effect on breast cancer risk,
raising it 3 1/2 to 5 times higher than normal. These types of lesions include:
- Atypical ductal hyperplasia (ADH)
- Atypical lobular hyperplasia (ALH)
Women with a family history of
breast cancer and either hyperplasia or atypical hyperplasia have an even
higher risk of developing a breast cancer.
In lobular carcinoma in situ
(LCIS) cells that look like cancer cells are growing in the lobules of the
milk-producing glands of the breast, but they do not grow through the wall of
the lobules. LCIS (also called lobular neoplasia) is sometimes
grouped with ductal carcinoma in situ (DCIS) as a non-invasive breast cancer,
but it differs from DCIS in that it doesn’t seem to become an invasive cancer
if it isn’t treated.
Women with this condition have a
7- to 11-fold increased risk of developing invasive cancer in either breast.
For this reason, women with LCIS should make sure they have regular mammograms
and doctor visits.
Women who have had more
menstrual cycles because they started menstruating early (before age 12) and/or
went through menopause later (after age 55) have a slightly higher risk of
breast cancer. The increase in risk may be due to a longer lifetime exposure to
the hormones estrogen and progesterone.
Women who, as children or young
adults, had radiation therapy to the chest area as treatment for another cancer
(such as Hodgkin disease or non-Hodgkin lymphoma) have a significantly
increased risk for breast cancer. This varies with the patient's age when they
had radiation. If chemotherapy was also given, it may have stopped ovarian
hormone production for some time, lowering the risk. The risk of developing
breast cancer from chest radiation is highest if the radiation was given during
adolescence, when the breasts were still developing. Radiation treatment after
age 40 does not seem to increase breast cancer risk.
From the 1940s through the 1960s
some pregnant women were given the drug diethylstilbestrol (DES) because it was
thought to lower their chances of miscarriage (losing the baby). These women
have a slightly increased risk of developing breast cancer. Women whose mothers
took DES during pregnancy may also have a slightly higher risk of breast
cancer.
Lifestyle-related factors and
breast cancer risk
Women who have had no children
or who had their first child after age 30 have a slightly higher breast cancer
risk. Having many pregnancies and becoming pregnant at a young age reduce
breast cancer risk. Pregnancy reduces a woman's total number of lifetime
menstrual cycles, which may be the reason for this effect.
Recent oral contraceptive use: Studies have found that women using oral contraceptives (birth
control pills) have a slightly greater risk of breast cancer than women who
have never used them. This risk seems to go back to normal over time once the
pills are stopped. Women who stopped using oral contraceptives more than 10
years ago do not appear to have any increased breast cancer risk. When thinking
about using oral contraceptives, women should discuss their other risk factors
for breast cancer with their health care team.
Depot-medroxyprogesterone
acetate (DMPA; Depo-Provera®) is an
injectable form of progesterone that is given once every 3 months as birth
control. A few studies have looked at the effect of DMPA on breast cancer risk.
Women currently using DMPA seem to have an increase in risk, but the risk
doesn’t seem to be increased if this drug was used more than 5 years ago.
Hormone therapy with estrogen
(often combined with progesterone) has been used for many years to help relieve
symptoms of menopause and to help prevent osteoporosis (thinning of the bones).
Earlier studies suggested it might have other health benefits as well, but
these benefits have not been found in more recent, better designed studies.
This treatment goes by many names, such as post-menopausal hormone
therapy (PHT), hormone replacement therapy (HRT), and menopausal
hormone therapy (MHT).
There are 2 main types of
hormone therapy. For women who still have a uterus (womb), doctors generally
prescribe both estrogen and progesterone (known ascombined hormone
therapy or HT). Progesterone is needed because estrogen alone can
increase the risk of cancer of the uterus. For women who no longer have a
uterus (those who've had a hysterectomy), estrogen alone can be prescribed.
This is commonly known as estrogen replacement therapy (ERT) or
just estrogen therapy (ET).
Combined hormone therapy: Using combined hormone therapy after menopause increases the risk
of getting breast cancer. It may also increase the chances of dying from breast
cancer. This increase in risk can be seen with as little as 2 years of use.
Combined HT also increases the likelihood that the cancer may be found at a
more advanced stage.
The increased risk from combined
hormone therapy appears to apply only to current and recent users. A woman's
breast cancer risk seems to return to that of the general population within 5
years of stopping combined treatment.
The
word bioidentical is sometimes used to describe versions of estrogen
and progesterone with the same chemical structure as those found naturally in
people. The use of these hormones has been marketed as a safe way to treat the
symptoms of menopause. It is important to realize that although there are few
studies comparing “bioidentical" or “natural” hormones to synthetic
versions of hormones, there is no evidence that they are safer or more
effective. The use of these bioidentical hormones should be assumed to have the
same health risks as any other type of hormone therapy.
Oestrogen therapy (ET): The use of oestrogen alone after menopause does not appear to
increase the risk of developing breast cancer. In fact, some research has
suggested that women who have previously had their uterus removed and who take oestrogen actually have a lower risk of breast cancer. Women taking estrogen
seem to have more problems with strokes and other blood clots, though. Also,
when used long term (for more than 10 years), ET has been found to increase the
risk of ovarian cancer in some studies.
At this time there appear to be
few strong reasons to use post-menopausal hormone therapy (either combined HT
or ET), other than possibly for the short-term relief of menopausal symptoms.
Along with the increased risk of breast cancer, combined HT also appears to
increase the risk of heart disease, blood clots, and strokes. It does lower the
risk of colorectal cancer and osteoporosis, but this must be weighed against
possible harm, especially since there are other effective ways to prevent and
treat osteoporosis.
Although ET does not seem to
increase breast cancer risk, it does increase the risk of blood clots and
stroke.
The decision to use hormone
therapy after menopause should be made by a woman and her doctor after weighing
the possible risks and benefits, based on the severity of her menopausal
symptoms and the woman's other risk factors for heart disease, breast cancer,
and osteoporosis. If a woman and her doctor decide to try hormones for symptoms
of menopause, it is usually best to use it at the lowest dose needed to control
symptoms and for as short a time as possible.
Some studies suggest that breastfeeding
may slightly lower breast cancer risk, especially if breastfeeding is continued
for 1½ to 2 years. But this has been a difficult area to study, especially in
countries such as the United States, where breastfeeding for this long is
uncommon.
One explanation for this
possible effect may be that breastfeeding reduces a woman's total number of
lifetime menstrual cycles (similar to starting menstrual periods at a later age
or going through early menopause).
The use of alcohol is clearly
linked to an increased risk of developing breast cancer. The risk increases
with the amount of alcohol consumed. Compared with non-drinkers, women who
consume 1 alcoholic drink a day have a very small increase in risk. Those who
have 2 to 5 drinks daily have about 1½ times the risk of women who don’t drink
alcohol. Excessive alcohol use is also known to increase the risk of developing
several other types of cancer.
Being overweight or obese after
menopause increases breast cancer risk. Before menopause your ovaries produce
most of your estrogen, and fat tissue produces a small amount of estrogen.
After menopause (when the ovaries stop making estrogen), most of a woman's
estrogen comes from fat tissue. Having more fat tissue after menopause can
increase your chance of getting breast cancer by raising estrogen levels. Also,
women who are overweight tend to have higher blood insulin levels. Higher
insulin levels have also been linked to some cancers, including breast cancer.
But the connection between
weight and breast cancer risk is complex. For example, the risk appears to be
increased for women who gained weight as an adult but may not be increased
among those who have been overweight since childhood. Also, excess fat in the
waist area may affect risk more than the same amount of fat in the hips and
thighs. Researchers believe that fat cells in various parts of the body have
subtle differences that may explain this.
Evidence is growing that
physical activity in the form of exercise reduces breast cancer risk. The main
question is how much exercise is needed. In one study from the Women's Health
Initiative, as little as 1.25 to 2.5 hours per week of brisk walking reduced a
woman's risk by 18%. Walking 10 hours a week reduced the risk a little more.
Many studies have looked for a
link between what women eat and breast cancer risk, but so far the results have
been conflicting. Some studies have indicated that diet may play a role, while
others found no evidence that diet influences breast cancer risk. Studies have
looked at the amount of fat in the diet, intake of fruits and vegetables, and
intake of meat. No clear link to breast cancer risk was found.
Studies have also looked at
vitamin levels, again with inconsistent results. Some studies actually found an
increased risk of breast cancer in women with higher levels of certain
nutrients. So far, no study has shown that taking vitamins reduces breast
cancer risk. This is not to say that there is no point in eating a healthy
diet. A diet low in fat, low in red meat and processed meat, and high in fruits
and vegetables might have other health benefits.
Most studies have found that
breast cancer is less common in countries where the typical diet is low in
total fat, low in polyunsaturated fat, and low in saturated fat. But many
studies of women in the United States have not linked breast cancer risk to
dietary fat intake. Researchers are still not sure how to explain this apparent
disagreement. It may be at least partly due to the effect of diet on body weight
(see below). Also, studies comparing diet and breast cancer risk in different
countries are complicated by other differences (like activity level, intake of
other nutrients, and genetic factors) that might also affect breast cancer
risk.
More research is needed to
understand the effect of the types of fat eaten on breast cancer risk. But it
is clear that calories do count, and fat is a major source of calories.
High-fat diets can lead to being overweight or obese, which is a breast cancer
risk factor. A diet high in fat has also been shown to influence the risk of
developing several other types of cancer, and intake of certain types of fat is
clearly related to heart disease risk.
Internet e-mail rumors have
suggested that chemicals in underarm antiperspirants are absorbed through the
skin, interfere with lymph circulation, cause toxins to build up in the breast,
and eventually lead to breast cancer.
There is very little evidence to
support this rumour. One small study found trace levels of parabens (used as
preservatives in antiperspirants and other products), which have weak
estrogen-like properties, in a small sample of breast cancer tumours. But this
study did not look at whether parabens caused the tumours. This was a
preliminary finding, and more research is needed to determine what effect, if
any, parabens may have on breast cancer risk. On the other hand, a large study
of breast cancer causes found no increase in breast cancer in women who used
underarm antiperspirants and/or shaved their underarms.
Internet e-mail rumors and at
least one book have suggested that bras cause breast cancer by obstructing
lymph flow. There is no good scientific or clinical basis for this claim. Women
who do not wear bras regularly are more likely to be thinner or have less dense
breasts, which would probably contribute to any perceived difference in risk.
Several studies have provided
very strong data that neither induced abortions nor spontaneous abortions
(miscarriages) have an overall effect on the risk of breast cancer.
Breast implants
Several studies have found that
breast implants do not increase the risk of breast cancer, although silicone
breast implants can cause scar tissue to form in the breast. Implants make it
harder to see breast tissue on standard mammograms, but additional x-ray
pictures called implant displacement views can be used to examine the
breast tissue more completely.
Breast implants may be linked to
a rare type of lymphoma called anaplastic large cell lymphoma. This lymphoma
has rarely been found in the breast tissue around the implants. So far, though,
there are too few cases to know if the risk of this lymphoma is really higher
in women that have implants.
A great deal of research has
been reported and more is being done to understand possible environmental
influences on breast cancer risk.
Compounds in the environment
that studies in lab animals have found to have estrogen-like properties are of
special interest. These could in theory affect breast cancer risk. For example,
substances found in some plastics, certain cosmetics and personal care
products, pesticides (such as DDE), and PCBs (polychlorinated biphenyls) seem
to have such properties.
This issue understandably
invokes a great deal of public concern, but at this time research does not show
a clear link between breast cancer risk and exposure to these substances.
Unfortunately, studying such effects in humans is difficult. More research is
needed to better define the possible health effects of these and similar
substances.
For a long time, studies found
no link between cigarette smoking and breast cancer. In recent years though,
some studies have found that smoking might increase the risk of breast cancer.
The increased risk seems to affect certain groups, such as women who started
smoking when they were young. In 2009, the International Agency for Research on
Cancer concluded that there is limited evidence that tobacco smoking causes breast
cancer.
An active focus of research is
whether secondhand smoke increases the risk of breast cancer. Both mainstream
and secondhand smoke contain chemicals that, in high concentrations, cause
breast cancer in rodents. Chemicals in tobacco smoke reach breast tissue and
are found in breast milk.
The evidence on secondhand smoke
and breast cancer risk in human studies is controversial, at least in part
because the link between smoking and breast cancer is also not clear. One
possible explanation for this is that tobacco smoke may have different effects
on breast cancer risk in smokers and in those who are just exposed to smoke.
A report from the California
Environmental Protection Agency in 2005 concluded that the evidence about
secondhand smoke and breast cancer is "consistent with a causal
association" in younger, mainly premenopausal women. The 2006 US Surgeon
General's report, The Health Consequences of Involuntary Exposure to
Tobacco Smoke, concluded that there is "suggestive but not
sufficient" evidence of a link at this point. In any case, this possible
link to breast cancer is yet another reason to avoid secondhand smoke.
Several studies have suggested
that women who work at night—for example, nurses on a night shift—may have an
increased risk of developing breast cancer. This is a fairly recent finding,
and more studies are looking at this issue. Some researchers think the effect
may be due to changes in levels of melatonin, a hormone whose production is
affected by the body's exposure to light, but other hormones are also being
studied.
Source: NHS Choices.
http://healthitis.blogspot.com
Source: NHS Choices.
http://healthitis.blogspot.com