Local management of early stage breast cancer and clinical risk prediction of survival

As local surgery is currently the most important component of curative breast cancer treatment, a large part of the study by focused on trends in breast surgery and survival following breast-conserving therapy and mastectomy. I n the Netherlands, the use of breast-conserving surgery had increased over time. Right after publication of landmark trials in 2002, demonstrating the safety of breast-conserving surgery, a steep rise in the use of breast-conserving surgery was seen. However, even after case mix correction, there was large variation between the nine Dutch regions. Part of this variation can be explained by unmeasured factors such as the patient’ and doctors’ preference or the degree of shared decision-making and are subject of further research. In the Dutch early stage breast cancer population, breast-conserving treatment led to at least equal overall, disease-free and breast cancer-specific survival as compared to mastectomy. This was confirmed in all subgroups based on age, tumour and nodal stage, receptor status, administration of adjuvant systemic therapy and presence of comorbidities. Besides, it was shown that starting radiation therapy as soon as possible after breast-conserving surgery did not affect survival rates. The second part of the study by Marissa van Maaren concentrated on clinical risk prediction of survival in breast cancer. First, the online prediction tool PREDICT was validated on the Dutch breast cancer population. The validation study showed that PREDICT accurately predicts overall survival in most Dutch breast cancer patients, but that results for should be interpreted cautiously in some specific patient groups. Furthermore, this thesis emphasised the importance of classifying patients according to breast cancer subtype, as these subtypes are independently related to survival and recurrence risks. In addition, the number of (disease-free) years survived (conditional survival) is a determining factor for the remaining risk of recurrences. CONCLUSIONS Breast-conserving treatment is at least equal to mastectomy in early stage breast cancer in terms of 10-year overall, disease-free and breast cancer-specific survival. Combined with results of randomised controlled trials, this thesis contributes to increased awareness that a mastectomy does not reduce the risk of recurrence and mortality, as compared to breast-conserving therapy. Besides, this thesis revealed the importance of specific risk profiles and use of conditional survival in clinical risk prediction. Overall, communication to patients, based on relevant data, plays a central role and should form the basis of the shared decision-making process. Ultimately, this will lead to better treatment decisions and more realistic risk perceptions