A) Mammography is not a perfect screening test, and understanding of its benefits and harms is incomplete

Some cancers will be missed, and some women will die of breast cancer regardless of whether they are screened.

Many cancers will be found, but most women diagnosed with breast cancer will be cured regardless of whether the cancer was found by a mammogram.

Some cancers that are found would have never caused problems. This is called overdiagnosis.

Often, women are called back for further testing because of an abnormality that is not cancer; this is called a false-positive result.

Studies of the benefits and harms of mammography have limitations and inconsistent results.

B) Benefits of mammography

Mammography decreases the number of women who will die from breast cancer. This benefit is greater for women who are at higher risk for breast cancer based on older age or other risk factors such as family history.

The number of women whose lives are saved because of mammography varies by age. For every 10 000 women who get regular mammograms for the next 10 years, the number whose lives will be saved because of the mammogram by age group is approximately: 5 of 10 000 women aged 40 to 49 years; 10 of 10 000 women aged 50 to 59 years; 42 of 10 000 women aged 60 to 69 years.

C) Harms of mammography

About half or more of women who have a mammogram yearly for 10 years will have a false-positive mammogram, and up to 20% of these women will need a biopsy.

For some women undergoing regular screening, the mammogram may find an invasive cancer or noninvasive condition ( ie, ductal carcinoma in situ ) that would never have caused problems ( overdiagnosis ).
Experts are uncertain of how frequently this happens, but estimates suggest that if a woman undergoing a screening mammogram is diagnosed with cancer or ductal carcinoma in situ, there is about a 19% chance that the cancer is being overdiagnosed, and she will receive unnecessary treatment.

D) Making a decision about mammography

Experts recommend that women aged 50 to 74 years undergo a screening mammogram every 2 years.
Whether a woman may benefit from starting mammograms earlier or having them more frequently depends on her risks for breast cancer.

Each woman may feel differently about the possibility of having a false-positive result or being diagnosed with and treated for cancer that might not have caused problems.
It is also important to consider how a woman might feel if she decides not to undergo screening mammography and she is later diagnosed with breast cancer, even if the likelihood that mammography would have made a difference is small. ( Xagena )

Source: JAMA, 2014

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