Tomosynthesis: a new tool against breast cancer

Approved by Health Canada in 2011, tomosynthesis, or 3D mammography, is a new digital imaging tool that allows structures inside the breast to be visualized by capturing multiple X-ray images from different angles. The computer converts the data into a series of thin layers, enabling a more accurate analysis of the size, shape and location of abnormalities.

For breast cancer screening, tomosynthesis is usually combined with 2D mammography. It can also be used to provide a diagnostic assessment following an abnormal mammogram, or if there is a physical disorder such as a nodule, discharge or changes in the skin.

As with mammography, tomosynthesis involves an X-ray machine, but not a stationary one. Multiple X-rays are taken from different angles, via an X-ray tube that moves in an arc over each breast. The X-rays are then synthesized by computer to create three-dimensional images.

This examination also requires that the breasts be compressed, to obtain a quality image and reduce the amount of radiation exposure. However, tomosynthesis images can be captured at the same time and on the same machine as 2D mammograms, thereby reducing examination times and avoiding the need to compress the breasts again. As for the radiation emitted by mammography and tomosynthesis combined, the total dose does not exceed recommended standards.

By displaying one thin layer of tissue at a time, tomosynthesis makes it possible to detect more tumours that may be concealed during 2D mammography due to overlapping or dense tissue.

According to the Canadian Association of Radiologists and the Canadian Society of Breast Imaging, tomosynthesis detects between one and two cases per 1,000 more than 2D mammography. In addition, it is thought to reduce false positives, i.e. the recall rate for further screening examinations, by 30 to 40%.[1]

When an X-ray passes through several dense but benign structures, such as cysts, the images can create the illusion of a mass, resembling a tumour. This is known as a false positive.

In its opinion on breast tomosynthesis and breast cancer screening in 2019, the Institut national d’excellence en santé et en services sociaux (INESSS) made the same observation about the efficacy of tomosynthesis for detecting breast cancer. However, the data do not allow us to say whether overdiagnosis is involved, i.e. whether the cancers detected would have caused symptoms or death.[2]

Consequently, further studies are needed to determine whether tomosynthesis reduces the number of deaths attributable to breast cancer. Despite this, tomosynthesis remains an indispensable tool for both breast cancer screening and diagnosis.

Tomosynthesis is not included in the Quebec Breast Cancer Screening Program because there are still not enough studies to justify its widespread use. However, this promising technology may be helpful for young women and people at risk, particularly those with dense breasts, because lesions hidden in the breast tissue are more likely to go undetected.

The procedure may also be indicated when an abnormality is detected, as it improves the detection of architectural distortions and enables better characterization of masses and asymmetries of density.

Considering the possible benefits of tomosynthesis, ask your doctor or radiologist whether this examination might be appropriate in your case. The costs are covered by the Régie de l’assurance maladie du Québec.

We offer services that can help your doctor detect breast cancer as early as possible..

• Mammogram

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