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Breast cancer facts and risk factors
How common is breast cancer?
Breast cancer is the cancer diagnosed most frequently in
North American women. About 200,000 new cases are diagnosed
in American and Canadian women and men each year and
nearly 65,000 women die from the disease each year in
the USA and Canada.
What is my risk of developing breast cancer?
One statistic that is often quoted is that women have a 1 in 9,
or even a 1 in 8 chance of developing breast cancer. This number
is alarming and needs explanation. It is true that a woman has a
1 in 9 (or 11%) chance of developing breast cancer, but this is
true only if she lives to the age of 90.
Other factors that add to the risk of developing breast
cancer include the following:
Strong increased risk (greater than 4 times normal)
- female gender
- advancing age
- previous cancer in one breast (especially lobular carcinoma)
- family history of breast cancer: pre-menopausal or in both breasts
- past breast biopsy showing severely abnormal cells and hyperplasia
Moderate increased risk (2 to 4 times normal)
- over 30 years old at birth of first child
- past breast biopsy: any sign of cell abnormality or hyperplasia
- post-menopausal obesity
- diet (possibly)
Weak increased risk (up to 2 times normal)
- first menses before the age of 12 years
- menopause after the age of 54 years
- family history of breast cancer: older post-menopausal
- prolonged hormone use (more than 15 years)
- moderate to heavy alcohol consumption
Risk factors that increase your chances of developing breast cancer:
Family history
A single case of breast cancer among close relatives (mother, sisters,
daughters, grandmothers, and aunts) only increases your personal risk a
small amount, especially if the cancer was diagnosed when your relative
was over 50 years old. However, the risk of a hereditary predisposition
to cancer is higher if there are several cases of breast cancer in your
family. This is especially true if any cases were diagnosed before age 50,
or if anyone had cancer in both breasts.
Your menstrual and reproductive history
Prolonged exposure to estrogen increases your chance of developing
breast cancer. Estrogen stimulates the cells in the breasts' milk
ducts, from which cancers develop. The risk of breast cancer is increased:
- if your periods started early (before age 12) and ended
late (after age 56)
- if you have not been pregnant - however, an early first
full-term pregnancy (before age 20) seems to have a protective
effect on the cells in the milk ducts, and such women have a
lower-than-average risk of breast cancer
- if you have used estrogen after menopause for a long time,
more than 5 to 10 years, this weakly increases the chance of
breast cancer
Previous breast biopsies
Most benign or fibrocystic changes seen in a breast
biopsy are not indicators of future cancer. However,
if the cells in the normal milk ducts are beginning
to look abnormal (called atypia) or heap up in an
abnormal number (called hyperplasia), the risk
of developing breast cancer later is increased by a modest amount.
Lifestyle
The North American lifestyle results in higher rates
of breast cancer than the lifestyles in Africa or Asia.
This may be due to differences in menstrual and
reproductive patterns, but affluence and diet are also likely important.
Diet
Regularly drinking more than 2 alcoholic drinks
a day and obesity after menopause have been linked
to higher rates of breast cancer. It is hard to define
a specific "good" or "safe" diet, but emphasizing green
and yellow fruits and vegetables, reducing the number
of total calories consumed, and exercising regularly
to achieve an ideal body weight are most likely to be helpful.
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