A mammogram may help find cancer early. But finding cancer early doesn't always save lives. In some cases the cancer will have already spread to other parts of the body.
A mammogram may appear to detect a cancer even when a cancer is not present (false-positive results). This can occur at any age but is more likely with younger women. False-positive results can lead to emotional distress and unneeded tests and treatments.
A mammogram may miss finding breast cancer even when it is there (false-negative results). This is more likely to happen with young women who have dense breasts. False-negative results can keep a woman from getting treatment and can give her a false sense of security.
Also, mammograms may find certain types of breast cancer that would never cause symptoms or threaten a woman's life. But doctors cannot tell what kinds of cancer will cause problems, so all cancers are treated. This means that women may end up having tests and treatments they don't need. These can cause harm.
There is always a slight risk of damage to
cells or tissue from being exposed to any radiation, including the very low
levels of radiation used for this test. But the risk of damage from the X-rays
is very low compared with the potential benefits of the test.