The aim is to add to what is known about the potential of personalized screening based on prior screening outcomes.
BreastScreen Norway is a public health service, and invites all women in Norway between 50 and 69 years to have a screening mammogram (x-ray image of the breast) every other year.
On most of the attending women's mammograms, there are no findings, and we say that these women are screened negative. Actually, only 3% of women attending BreastScreen Norway have uncertain or suspicious findings on their mammograms. These women are recalled for additional assessment. Among women recalled, three out of five are evaluated negative (healthy) after additional imaging, without any additional tests. A needle biopsy is required for the remaining two out of five recalled women.
This means that a small group of women is selected for a needle biopsy. About half of these women have breast cancer or a precursor requiring treatment. The other half shows a wide spectrum of benign results, from normal cells via atypical cell changes to in situ lesions. In situ lesions are cells that have initiated a possible development towards breast cancer, but where the changes are located only within the milk ducts or breast lobule.
This postdoctor project is part of a larger project where researchers from different disciplines are working together to add to what is known about benign findings in the breast and precursors of breast cancer. The project may contribute in identifying the optimal follow-up for women with different types of findings from prior screening(s), and may increase our knowledge about the process where normal cells develop into breast cancer. The project may also contribute to increased knowledge about overdiagnosis and overtreatment of breast cancer.
All women recalled for additional imaging in BreastScreen Norway have in common that something on their mammograms prompted the radiologists to have a second look. We know from previous studies that this group of women has an increased long term risk of breast cancer. The first step of this project was to make more systematic and precise estimates of the risk of progression for different types of benign findings and precursors to breast cancer. The second step is to investigate how the risk of progression depends on epidemiological risk factors among women with prior mammographic findings.
We, and many other researchers worldwide, show special interest for the precursors of breast cancer where cells have initiated a progression towards breast cancer within the milk ducts, Ductal Carcinoma In Situ (DCIS). Today, all Norwegian women diagnosed with DCIS are treated surgically, often also with radiation treatment, due to their increased risk of developing breast cancer if left untreated. Researchers in the US, Great Britain, Belgium and the Netherlands are currently running ground-breaking studies of watchful waiting in order to identify subgroups of women with this diagnosis who may not need treatment. This could be the case for DCIS lesions where the cell changes only to a small degree are similar to the changes seen in invasive breast cancer. As part of our project, we are organizing a radiological review where radiologists are evaluating selected characteristics of screening mammograms showing DCIS. The aim of our subsequent analysis is to identify mammographic features predicting higher or lower risk of developing invasive breast cancer.
Planned studies and status
Study 1: Estimate the risk of developing invasive breast cancer among Norwegian women with prior benign breast disease or a premalignant lesion, for different types of lesions and compared to women who are screened negative.
Number of prior negative screening outcomes does not influence future risk of breast cancer. Lilleborge M. et al, Eur J Epidemiol. 2020 Jun;35(6):549-556.
Risk of breast cancer by prior screening results among women participating in BreastScreen Norway. Lilleborge M. et al, Cancer. 2019 Oct 1.
Study 2: Identify epidemiological risk factors of progression to invasive breast cancer among women with prior benign breast disease or premalignant lesion. In progress.
Study 3: Identify mammographic features on initial screening mammograms showing DCIS which predict an increased [or decreased] risk of progression to invasive breast cancer. In progress.
The project is carried out by Marie Lilleborge (PhD) and section for breast cancer screeening at the Cancer Registry of Norway.
Mentors and supervisors of this project are Solveig Hofvind, head of the Mammography section at the Cancer Registry of Norway and Professor of radiography at Oslo Metropolitan University, and Giske Ursin, Director of the Cancer Registry of Norway.
External collaborators include:
- Ragnhild Sørum Falk, Oslo University Hospital
- Therese Sørlie, Oslo University Hospital
- Hege Russnes, Oslo University Hospital
- Torill Sauer, Akershus University Hospital
- Marit Muri Holmen, Oslo University Hospital
- Tone Bøe Aaman Vamre, Oslo University Hospital
- Elisabete Weiderpass, International Agency for Research on Cancer (IARC)
- Ellen Schlichting, Oslo University Hospital
- Vessela Kristensen, Oslo University Hospital
- Anne-Lise Børresen-Dale, Oslo University Hospital
- Gry Geitvik, Oslo University Hospital
- Åslaug Helland, Oslo University Hospital
- Vilde Drageset Haakensen, Oslo University Hospital