Is there any evidence that breast screening can increase the chances of getting cancer?

The short version: mammography can cause breast cancer through radiation, but the number of cancers caused is small compared to the number of deaths prevented in older women, and the balance is worse for younger women and those with BRCA mutations.

The evidence in this retrieval is clear on one mechanism: mammography uses ionizing radiation, and radiation is a known cause of breast cancer. A 2011 study estimated that annual screening from age 40 to 74 would cause about 86 radiation-induced cancers and 11 deaths per 100,000 women screened [5]. A separate 2014 study put the risk even lower for biennial screening from age 50 to 69, estimating about 10 induced cancers and 1 death per 100,000 women [6]. The younger the woman at first exposure, the higher the risk: a 2017 systematic review found that BRCA mutation carriers face a potentially elevated risk from mammography, especially if exposed before age 30, and recommended MRI-based screening instead [7]. A 2005 UK study calculated that screening women aged 50-69 prevented about 58 deaths for every cancer it caused [8].

But radiation is not the only way screening can harm. The bigger problem is overdiagnosis: finding cancers that would never have caused symptoms or death. A 2018 model of Norwegian screening data found that the observed 38% increase in incidence could not be explained by lead-time alone and required 10-14% overdiagnosis [3]. A 2017 critique estimated overdiagnosis at about 30% of screen-detected cancers [4]. That means for every woman whose life is saved by screening, several others are treated for a cancer that would never have hurt them. Treatment for breast cancer - surgery, radiation, chemotherapy - carries its own risks of heart damage, second cancers, and death.

The evidence here does not include a single long-term randomized trial comparing screened to unscreened women on all-cause mortality. The mortality reductions claimed (about 50% in simulation models [1]) come from modeling studies, not from direct head-to-head trials. The 2012 commentary in this retrieval warns that case-control studies overestimate benefit due to self-selection bias, and that even incidence-based mortality studies can be confounded by treatment improvements [2].

My call: mammography screening causes a small number of radiation-induced breast cancers, and a much larger number of overdiagnosed cancers that lead to unnecessary treatment. For women over 50, the mortality benefit likely outweighs the radiation risk, but the overdiagnosis problem means many women are harmed by treatment they did not need. For women under 40 and for BRCA carriers, the risk-benefit is worse and the evidence does not support routine mammography. Confidence: moderate.