"Since the first report last year, the number of cancers detected by AI-supported screening has gone from being 20 per cent more to 29 per cent more than those found by traditional screening," says Kristina Lång, researcher and associate professor of diagnostic radiology at Lund University, Sweden and consultant at the Unilabs Mammography Unit in Malmö.
Every year, around one million women are called for mammography screening in Sweden. The mammogram are reviewed by two breast radiologists - a medical skill that is currently in short supply. In the MASAI trial, AI had to identify mammograms with an increased risk of breast cancer. These cases were then reviewed by two breast radiologists. Other mammograms were only reviewed by one breast radiologist. In all these cases, the radiologist(s) was/were assisted by AI, which highlighted suspicious findings on the image.
The new research report is based on results from almost 106,000 women screened for breast cancer. Half of them were randomly assigned to undergo traditional mammography screening, while the other half received AI-supported screening. AI-supported screening was found to pick up not only more cancers overall (in 338 people compared with 262) but also 24 per cent more early-stage invasive cancers (in 270 people compared with 217).
"They also included relatively more aggressive cancers that are particularly important to detect early. At a later stage, the prognosis may have deteriorated and more intensive treatment is often required," says Kristina Lång, pointing to potential benefits in terms of reduced suffering, higher survival rates and lower economic costs if these cancers can be detected more frequently at an early stage.
Pre-cancerous lesions, known as in situ cancers, were also more likely to be detected with AI - 51 per cent more such cases were found (68 people compared with 45). A large proportion of the additional in situ cases found were of the more severe type which also benefits from early detection.
Importantly in this context, the number of false positives did not rise despite an increase in cancer detection.
"A false positive is when a woman is recalled for work up but is then found not to have cancer. This can be a stressful experience for women participating in screening. But only seven more people, corresponding to a one per cent increase, received these false alarms in the AI-supported group compared with the control group," says Kristina Lång.
As in the previous report from last year, AI-supported screening was again found to significantly reduce breast radiologists’ workload by 44 per cent.
Sweden has a generous screening programme by international standards. All women aged 40-74 years are invited for a mammogram every 1.5-2 years. However, the interval between two screening visits can be long enough for cancer to be diagnosed - even if the last screening was considered normal. These so called interval cancers is the next group of cancers that Kristina Lång and her colleagues will analyse.
"This December, the 106,000 women have been followed up for two years, allowing researchers to see how common it is to receive a breast cancer diagnosis between two screening visits. Our hope is that AI will prove helpful here too," says Kristina Lång.
Results from the MASAI trial have already contributed to the implementation of AI support in several regional screening programs in Sweden.
Hernström V, Josefsson V, Sartor H, Schmidt D, Larsson AM, Hofvind S, Andersson I, Rosso A, Hagberg O, Lång K.
Screening performance and characteristics of breast cancer detected in the Mammography Screening with Artificial Intelligence trial (MASAI): a randomised, controlled, parallel-group, non-inferiority, single-blinded, screening accuracy study.
Lancet Digit Health. 2025 Feb 3:S2589-7500(24)00267-X. doi: 10.1016/S2589-7500(24)00267-X
* The MASAI trial has been funded with support from the Swedish Cancer Society, Lund University/ALF, the Confederation of Regional Cancer Centres and MAS Cancer.