Jacky Luiten

144 | Valorization The national breast cancer screening program is a free of charge biennial screening mammography for women aged 50 ‐ 75 years. 1,2 Yearly, approximately 1.3 million women are invited to the nationwide breast cancer screening program in the Netherlands, of whom almost 1 million women participate. Ever since the introduction of the screening program there has been a broad support among Dutch women, which is expressed by an attendance rate of approximately 80%. 3 After its introduction many scientific papers have reported about the favorable results of the screening program. Detection of the disease in a less advanced stage will improve the prognosis and allows a less extensive and aggressive treatment with less side ‐ effects. 4 ‐ 6 In an effort to detect breast cancer in its earliest phase any breast abnormality found at screening mammography is examined in close detail, which has resulted in a sharp increase in the detection rates of DCIS and other pre ‐ malignant diseases. A substantial part of these pre ‐ malignant abnormalities may not proceed into invasive breast cancer during a woman’s lifetime, 7,8 and part of them may even regress spontaneously. 9 From the aforementioned we can conclude that the diagnosis and subsequent treatment of pre ‐ malignant lesions may not be necessary in some women and could be seen as overtreatment, thereby creating avoidable morbidity. 10 ‐ 12 Another downside of screening mammography which must not be overlooked are the false positives recalls, which not only cause extra medical costs and psychological stress, but also a potential burden of subsequent unnecessary invasive biopsies. 13 A careful consideration of the harm ‐ benefit balance associated with breast cancer screening continues to be a matter of debate. This thesis provides a substantiated contribution to the discussion about overtreatment, because it creates more awareness of the magnitude of the problem. Moreover, this thesis helps clinicians to safely refrain from interventions and form the basis for further research in order to combat overdiagnosis and subsequent overtreatment. Social and economic relevance This thesis provides additional evidence for the beneficial effect of screening mammography programs. Our study shows that screen ‐ detected DCIS was mainly high grade in contrast to invasive carcinomas which were mainly found to be low or intermediate grade. This observation suggests that treatment of poorly differentiated DCIS detected through mammographic screening could play a role in the relative reduction of the incidence of poorly differentiated invasive carcinoma, assuming that high ‐ grade DCIS was removed before it could develop into high ‐