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This animation explains the likelihood that going for breast screening will
lead you to have treatment for breast cancer that would never have caused
problems during your lifetime.
The numbers given are based on estimates made by experts
and have been rounded up for simplicity.
In an earlier animation, we compared survival from breast cancer in 200 women
who DID go for breast screening compared with 200 women who DID NOT.
Let’s look at those groups again.
About 3 more women will be diagnosed with breast cancer over the 20 year period in the
group that go for breast screening. These are true breast cancers picked up by the mammogram.
In the group of women who do NOT go for breast screening, these 3 breast cancers
are not picked up. This is because, unlike most breast cancers, these ones never become
big enough to cause symptoms. These women will never know they have breast cancer
and it doesn’t cause any problems in their whole life.
If they had gone for breast screening, these cancers would have been discovered.
All the women diagnosed with breast cancer will receive treatment. So that’s 12 women
in the group who DON’T go for breast screening, and 15 women in the group
who DO go for breast screening.
So, it is estimated that about 3 women receive treatment that they would have avoided if
they had not gone for breast screening. This is called over-treatment.
So why were these women given treatment?
Most breast cancers WOULD cause symptoms or death if left untreated, but some would not.
Currently, doctors cannot say for sure which breast cancers would never grow or cause
problems. For this reason, they always recommend treatment to women.
To recap, the chances are that for every 15 women who receive treatment for a breast
cancer detected through screening, about 3 did not need that treatment, while 12 did.
Importantly, it is NOT possible to say which women definitely DID NOT need treatment.
The chance of being over-treated is the main risk of breast screening.