Understanding Breast Cancer Risk
All women are at risk for getting
breast cancer. As you get older, your risk increases. Assuming you live to age
90, your risk of getting breast cancer over your lifetime is about 14%. That
might sound scary, because it means that an average of about one out of every
seven women will get breast cancer over a 90-year life span.
You can also look at it another way: A 14% risk means there's an 86%
chance that you WON'T get breast cancer.
How Much Do Risk Factors and
Preventive Factors Change Your Risk?
Knowing what factors can increase or decrease your risk for breast cancer
is important. But you probably want to know just HOW MUCH those factors change
your risk.
If you hear that a certain treatment can reduce your risk by 40%, what
does that mean?
To understand what the numbers mean about YOUR risk for breast cancer, the
key terms to know are relative risk and absolute risk.
Relative risk is the
number that tells you how much something you do, such as taking a pill, can
change your risk, compared to your risk without taking that pill. Relative risk
can be expressed in percentages and in "hazard ratios." If you do
nothing new, your hazard ratio is 1.0—this means that your risk doesn't
change. If you do something and your risk decreases by half, or goes down to
0.5, then you are half as likely to have the risk. But if your risk goes up,
from 1.0 to 1.88, then you are 88% more likely to encounter the risk. If your
risk goes up to 3.0, then you have a threefold (300%) increased risk of having
the problem.
Absolute risk is the
size of your own risk. Absolute risk reduction is the number of percentage
points by which your own risk changes if you do something, like taking a pill.
The size of your absolute risk reduction depends on what your risk is to begin
with.
Example of Risk Going Up for a
Woman with No History of Breast Cancer
Smoking is associated with an increased risk of breast cancer as well as
other diseases.
Suppose your risk of breast cancer is 14%. If you smoke, your risk goes up
by 32% (about a third higher risk). That means your risk of breast cancer from
smoking is 32% higher than the 14% risk if you don't smoke. That's the relative
risk increase from smoking.
But how big a difference does a 32% increase really make for you? To
figure out the change to your absolute risk, see what happens when you make your
risk of 14% go up by a third:
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- Multiply your risk of 14% by
the relative risk increase of 32%. You get 4% (14% x 32% = 4.48%, or 4%). 4% is
the size of the increase in risk.
- Add the 4% increase to the 14%
risk you started out with, and you end up with 18% risk (14% + 4% = 18%),
| That means your absolute risk for breast
cancer is 18% if you have no history of the disease and you smoke.
Example of Risk Going Down for
a Woman with Breast Cancer History
Suppose you have had breast cancer and had lumpectomy with clear margins
(meaning no cancer was found between the tumor and the edge of the surrounding
tissue that was removed along with it).
After lumpectomy with clear margins, your risk of the breast cancer coming
back in the same breast is about 30%. But if you choose to have radiation
therapy after your lumpectomy, you can reduce your risk of the cancer coming
back by two-thirds or 66%. This is the relative risk decrease.
But how much of a difference does radiation's 66% drop really make? To
figure out the change to your absolute risk, take two-thirds off your risk of
30%:
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- Multiply your risk of the
cancer coming back (30%) by the relative risk decrease from radiation therapy
(66%), and you get a decrease of 20% (30% x 66% = 19.80% or 20%).
- To figure out your remaining
risk of recurrence after radiation, subtract the 20% from the 30% risk of
recurrence that you started out with (30% - 20% = 10%). So your absolute risk of
the cancer coming back falls to 10% if you have radiation therapy.
| Now, after lumpectomy and radiation, is
there something else you can do to knock down the 10% risk further? You may also
choose to take hormonal therapy (for example, tamoxifen or an aromatase
inhibitor) for five years. Learn more about hormonal therapy choices. If you do
that, you can reduce your risk by another 50%. By taking hormonal therapy for
five years, you lower your relative risk of the cancer coming back in the same
breast by half or 50%. To see how big a difference hormonal therapy makes in
your absolute risk, take half off your risk:
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- Multiply your risk by the
relative risk decrease from tamoxifen (10% x 50% = 5%).
- Then subtract that 5% from
your risk (10%–5% = 5%).
| Now your absolute risk of the cancer
coming back is 5%. So by having radiation therapy and taking hormonal therapy
for five years, you have reduced your risk of the breast cancer recurring from
30% to 5%.
Knowing how much your breast cancer risk changes with
lifestyle changes and treatment options can help you and your doctor make the
best decisions for YOU.
Risk
Factors You Can Control
Many factors might affect your risk for breast cancer and other
diseases. You may be able to control and modify some of these, including:
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- what you eat,
- how much you weigh, and
maintaining a healthy weight,
- how much you exercise,
- whether you smoke,
- whether you drink alcohol and
if so, how much and how frequently,
- the types of chemicals in your
environment, and
- whether you took hormone
replacement therapy (HRT) for menopausal symptoms for five years or longer
| Making these changes in your life can be
quite difficult. But it becomes easier to make these changes when you understand
each factor, the importance of the changes, and practical ways to make the
changes. And when it comes to the factors that can't be controlled, we'll help
you work around them.
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