Is breast cancer overdiagnosed by mammography screening?

What is overdiagnosis and how often does it happen?

Overdiagnosis is not a false positive (a suspicious finding that turns out to be nothing). It is a true cancer diagnosis — but one that would never have caused problems in the woman's lifetime. The cancer either grows so slowly it would never become symptomatic, or the woman would die of another cause before it ever did. The result is unnecessary treatment: surgery, radiation, chemotherapy, and lifelong anxiety.

How common is it? A 2023 systematic review and meta-analysis of 30 studies found that, among women 40 and older, about 12.6% of breast cancers detected by mammography are overdiagnosed [6]. That means roughly 1 in 8 screen-detected cancers is one that didn't need to be found. A separate 2022 analysis using U.S. data from the Breast Cancer Surveillance Consortium estimated that for women 50-74 screened every two years, about 15.4% of screen-detected cancers — roughly 1 in 7 — are overdiagnosed [3]. Both studies converge on a similar range, and the 2023 meta-analysis is the largest and most comprehensive of these, pooling data from many studies.

Does overdiagnosis vary by age?

Yes, strongly. The risk of overdiagnosis rises sharply with age. A 2023 study of women 70 and older in U.S. Medicare found that among women 70-74, an estimated 31% of screen-detected cancers were overdiagnosed. For women 75-84, that figure rose to 47%. And for women 85 and older, it reached 54% [1]. The same study found no statistically significant reduction in breast cancer deaths from screening in these older age groups. This makes intuitive sense: older women have a higher chance of dying from something else before a slow-growing cancer would ever matter.

For younger women, the numbers are lower but not zero. The 2023 meta-analysis covering women 40 and older found a 12.6% overall overdiagnosis rate [6]. A European systematic review for the European Commission found overdiagnosis probabilities of 17% for women 50-69 and 23% for women under 50 [4]. So while the benefit of screening (reducing breast cancer death) is clearer for women in their 50s and 60s, the harm of overdiagnosis is present at every age and becomes dominant in older age.

How does overdiagnosis compare to the benefit of screening?

This is the central trade-off. A 2022 Norwegian study calculated that, assuming a 20% reduction in breast cancer mortality from screening and a 20% overdiagnosis rate, for every breast cancer death prevented, 5.4 women were overdiagnosed in 2016 — and that ratio has been getting worse over time as treatments improve [5]. If the mortality benefit is smaller (8.7% reduction), the ratio jumps to 14 overdiagnosed women per death prevented. If the benefit is only 5%, it's 25 overdiagnosed women per death prevented.

The landmark 2017 New England Journal of Medicine study by Welch et al. put it bluntly: after mammography became widespread, the number of small tumors detected increased dramatically (162 more per 100,000 women), while the number of large tumors decreased only modestly (30 fewer per 100,000). They concluded that women were more likely to have breast cancer that was overdiagnosed than to have earlier detection of a tumor destined to become large [8]. They also estimated that improved treatment, not screening, accounted for at least two-thirds of the reduction in breast cancer mortality.

The Cochrane review, updated in 2024, is the most authoritative summary of the randomized trials. It found that the adequately randomized trials did not show a statistically significant reduction in breast cancer mortality (risk ratio 0.90, 95% CI 0.79 to 1.02) and that screening did not reduce total cancer mortality or all-cause mortality [2]. The review concluded that breast screening 'does not meet the criteria that population screening should be based on rigorously performed randomised trials that show that the benefits outweigh the harms.'

What does this mean for a woman deciding about screening?

The evidence is clear that overdiagnosis is a real and substantial harm of mammography screening. For women in their 50s and 60s, the balance of benefits and harms is most favorable — screening reduces breast cancer death by about 23% according to the European review [4], but at the cost of a 17% chance of overdiagnosis if cancer is found. For women under 50, the benefit is smaller and the overdiagnosis risk is similar. For women over 70, the benefit is uncertain and the overdiagnosis risk is high — 31% to 54% [1].

The key takeaway is that screening is a choice, not a moral obligation. Women should be informed that for every woman whose life is saved by mammography, several others will be diagnosed and treated for a cancer that never would have harmed them. The decision should factor in age, overall health, and personal values about the trade-off between a small chance of benefit and a real chance of harm. Several of the studies here explicitly call for shared decision-making and better risk communication [4][7].

About These Sources

This answer is built on 8 peer-reviewed studies — published from 2017 to 2024, 1 from 2024 or later, 3 in Q1 journals, collectively cited 278 times — selected as the most relevant from 14 studies that passed quality screening, drawn from 44 papers retrieved from a database of over 500 million.

Sources used in this answer

Related research questions