(NBC News) Each year thousands of women find themselves undergoing a mammogram, hoping a few moments of discomfort will help them avoid breast cancer.
But no cancer screening is foolproof, and a new review of mammogram studies spanning the past 50 years reaffirms this.
"These studies, when you look at them as a whole, suggest there is a benefit to screening mammography that's probably about equal to a 19% reduction in the risk of dying of breast cancer," says Dr. Nancy Keating of Harvard Medical School.
It's a benefit that researchers say has to be weighed against the potential harms.
They found that one in five breast cancers spotted during annual screening may be over-diagnosed, meaning that cancer will never grow and threaten the woman's life.
They also found more than half of women will have at least one false positive.
"Most of these false positives just require women to come back for additional testing done, additional images and sometimes they require a biopsy," Dr. Keating explains.
Doctors say new drugs and treatments are the reasons most women are beating cancer today, not mammograms.
"Current breast cancer treatment is so effective that the vast majority of women will survive regardless of how or when their breast cancer is diagnosed," Keating says.
The study found mammograms have a greater benefit for women in their 50s and 60s, but outside experts say this does not mean women in their 40s should skip the test.
While more women in this age group need to be screened to save one life, many are willing to bear any potential harm for the chance that life saved is theirs.
Researchers say the mammogram is not perfect, but it is still the only screening tool we have.
This study was designed to help doctors relay the risks and benefits to their patients, and help them come up with an individual treatment plan.
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