DCIS consists of aberrant cells in the milk ducts of the breast. About 2,300 women are diagnosed with this condition a year in the Netherlands, of which approximately 80% are discovered during breast cancer screening. This is because the calcium splashes that could indicate DCIS can be seen on a breast x-ray (mammogram).
It still is not possible to predict which DCIS will progress to breast cancer and which will not, however, which means that virtually all women with DCIS receive preventive treatment consisting of a mastectomy or breast-conserving surgery followed by radiation and, in some countries, hormone therapy. As a result, tens of thousands of women around the world undergo intensive treatment – including the disadvantages – without any benefits. To prevent overtreatment in the future, researchers at The Netherlands Cancer Institute and the VIB-KU Leuven Center for Cancer Biology have developed a "living biobank" of DCIS cells to better understand their progression to cancer.
The development from DCIS to breast cancer in humans usually takes 10 to 20 years. In the new mouse models in which human DCIS cells are inserted, this development only takes one year. It is difficult to study DCIS in patients themselves because DCIS is surgically removed fairly soon after diagnosis.
Researchers at the Netherlands Cancer Institute developed more than 100 different DCIS mouse models that allow them to accurately follow the progression from DCIS to breast cancer. DCIS cells from surgical tissue were introduced into the milk ducts of mice under anesthesia, using a very thin needle. The growth of the different DCIS cells was then tracked over a period of one year, with just under half of the mice developing invasive breast tumors. Due to the time saved, this study allowed scientists to better understand why DCIS does, or – more importantly – does not develop into breast cancer.
Research leader Jos Jonkers from the Netherlands Cancer Institute: "Thanks to our mouse models, we were able to study DCIS live for the first time. This yielded a wealth of information that allowed us to bridge a gap spanning several decades between preclinical research and the clinic."
While transferring tissue from women with DCIS to mice was quite an achievement in itself, the results of the study are even more interesting. Thanks to the new mouse models, researchers have gained important information about breast cancer risk factors in DCIS. For example, molecular studies showed that the presence of the HER2 protein increases the risk of breast cancer. In contrast, presence of the protein to which the hormone estrogen can bind breast cancer meant a lower risk.