Personalizing breast cancer treatment with a focus on young women

In this dissertation entitled “Personalizing breast cancer treatment with a focus on young women”, we investigated in various ways how breast cancer treatment can be personalized using biomarkers. In part 1 we looked for prognostic biomarkers that can help select young patients with breast cancer who have such a good prognosis that they do not benefit from (neo)adjuvant systemic therapy (chapters 2 and 3). If systemic therapy is necessary, predictive biomarkers can help to identify which type of systemic therapy is most effective. In part 2 of this thesis we investigated predictive biomarkers and specifically biomarkers that demonstrate homologous recombination deficiency (HRD). Cancer cells that are HRD cannot repair breaks in their DNA. HRD can be tested in various ways, for example with the BRCA1-like test or by finding an error in the BRCA1 or BRCA2 genes. Chapter 4 describes the results of a phase II study into the effectiveness of the drug Niraparib in patients with metastatic breast cancer with HRD features. In chapter 5 we investigated whether we could find a specific mutation in breast or ovarian cancer with a methylated BRCA1 gene promotor. In chapter 6 we identified factors that can promote implementation of a new therapy. Together, these results contribute to improving the treatment of young people with breast cancer.