John Hilkens was group leader at the NKI from 1979 till 2016 after which he retired. His research focused on identifying genes that, when mutated, overexpressed or deleted, lead to breast cancer. To do this, he used a powerful technique called insertional mutagenesis in mouse models for human breast cancer. Once a cancer-causing gene was found, he investigated its function in the cell, particularly the molecular pathways it controls, which can become deregulated in cancer.