The incidence of cancer during pregnancy is estimated to be 1 to 2 in 1000 pregnancies. The most common cancer diagnosed during pregnancy is breast cancer. Over the past years, it has become clear that oncological treatment for maternal cancers during pregnancy is possible under well-defined circumstances. A study on the long-term outcome of 70 children exposed to chemotherapy in utero with a median age of 22.3 months reported normal development. Chemotherapy had no clear adverse effect on development but preterm birth was an independent predictor of poorer outcome. Over the course of this PhD project, we want to determine the long-term outcome of children prenatally exposed to maternal malignancy and oncologic therapy. The ultimate goal is to gain more knowledge about the developmental outcomes and to delineate the long-term safety of children exposed to maternal malignancy and treatment.