Why do two radiologists read each mammogram?
A mammogram is an X-ray of the breasts that can find cancer early, often before a lump can be felt. In the United States, a screening mammogram is usually read by one radiologist. Many European programs, like Sweden's, use double reading: two radiologists read the same exam separately, because two sets of eyes miss fewer cancers.
But there are not enough radiologists, and double reading takes a lot of time. That raises a simple question: can AI act as the second reader? Very few studies had tested this in real time, during actual screening.
How the ScreenTrustCAD study worked
The study took place at Capio Sankt Göran Hospital in Stockholm from April 2021 to June 2022. It included 55,581 women aged 40 to 74 who came in for routine screening and did not have breast implants. It was prospective: mammograms were read as they happened, in real life, not reviewed years later.
Each mammogram was read by two radiologists and by the AI. This let the researchers compare several reading strategies on the same women: two radiologists (the usual method), one radiologist plus AI, AI alone, or two radiologists plus AI. They counted cancers found through screening within 3 months. The goal was to check that the new approach does not find fewer cancers, which is called a non-inferiority study.
The results: 4% more cancers with one radiologist plus AI
In total, 269 women, or 0.5%, were diagnosed with breast cancer through screening. One radiologist plus AI found 261 cancers, compared with 250 for standard reading by two radiologists. That is 4% more cancers found, and no loss in detection.
AI alone, with no radiologist, found 246 cancers, a result judged non-inferior to the 250 found by two radiologists. All three readers together, two radiologists plus AI, found 269. For the authors, replacing one radiologist with AI is a serious option.
Key figures
- 55,581women aged 40 to 74 included in the study
- 261 vs 250cancers found by one radiologist plus AI versus two radiologists
- +4%more cancers detected when AI replaced one radiologist, with none missed
- 246cancers found by AI alone, a non-inferior result
Who reads your screening mammogram? Ask with Mima
This study does not change the exam itself: the mammogram feels the same, and a radiologist stays involved. What could change is who gives your images a second look.
Mima helps you keep track of your mammogram dates, your results and any callback for extra imaging. You can prepare a question for your imaging center: "Is my mammogram read by one radiologist, two, or with help from AI?"
What this could mean for women getting screened
If AI can act as the second reader, screening centers could free up radiologist time while finding at least as many cancers. For a woman, the exam itself does not change, and a radiologist stays involved.
The authors remain careful: they say AI could be introduced in a controlled way, with risk management and real-world tracking of its performance. For anyone getting screened, a fair question to ask is how their images are read.
The limits of this study
The study took place at a single Swedish hospital with one AI software. Women with breast implants were not included. The researchers counted cancers found within 3 months, so it is still unknown how many cancers show up between screenings, which requires longer follow-up.
The study also looked at false alarms, when women are called back for extra tests that turn out fine, and this matters as much as the number of cancers found. Finally, Lunit, a company that develops medical imaging AI, was among the funders.
Frequently asked questions
Can AI replace a radiologist in reading mammograms?
In this Swedish study, AI replaced the second of two readers without missing cancers. A radiologist was always still involved, and the authors call for a controlled rollout.
What is double reading in mammography?
It means two radiologists read the same screening mammogram separately. It is standard in Sweden and several other European countries.
Is AI used to read mammograms in the US?
This study did not look at the US. You can ask your imaging center how your mammogram is read and whether AI software is part of the process.
How is this different from the MASAI trial?
MASAI was a Swedish randomized trial that used AI to sort exams. ScreenTrustCAD compared several reading strategies, with and without AI, on the same women.
The original study
Dembrower K, Crippa A, Colón E, et al. “Artificial intelligence for breast cancer detection in screening mammography in Sweden: a prospective, population-based, paired-reader, non-inferiority study” The Lancet Digital Health, September 8, 2023. DOI : 10.1016/S2589-7500(23)00153-X
Read the full study in The Lancet Digital HealthThis article summarizes a scientific study and is not medical advice.