The road towards conquering DCIS overtreatment

The objectives of this thesis, aimed to reduce overtreatment of ductal carcinoma in situ (DCIS) of the breast, were : 1) to evaluate the risk of underestimation after a diagnosis of DCIS and the interrater reliability in the histopathological classification of DCIS, important conditions in order to safely adopt an active surveillance strategy for low-risk DCIS, 2) to investigate associations of clinicopathological factors with the risk of developing ipsilateral invasive breast cancer after treatment of DCIS and 3) to analyze the extent of response of DCIS, adjacent to HER2-positive breast cancer, to neoadjuvant systemic therapy and to investigate associations of clinicopathological factors with DCIS response.We have taken significant steps on the road towards conquering overtreatment of DCIS: by having identified several clinicopathological prognostic factors in pure DCIS, by providing reassuring evidence regarding underestimation in the context of active surveillance, by stressing the need for improvement of interrater reliability in histopathological classification, and by showing that the presence of DCIS adjacent to HER2-positive breast cancer should not preclude the option of breast conserving surgery.LUMC / Geneeskund