Children with cancer need a long term tunnelled central venous catheter (TCVC) for the entire duration of their treatment. TCVCs are locked with heparin when not in use. The most frequent complications of long term TCVC are catheter related blood steam infections. Taurolock is a new lock that is claimed to prevent the formation of luminal biofilm in TCVCs and has been demonstrated to eradicate infected CVCs. In this study the investigators will compare TCVCs locked with heparin with TCVCs locked with Taurolock. Hypothesis: Taurolock will diminish the number of CRBSI in children with cancer compared with children with heparin lock of their CVC.