To the editor,

With great interest have I read the recent contribution by Wintjens and colleagues providing a very thorough systematic review on drug delivery systems for the treatment of peritoneal carcinomatosis [1]—still one of the big challenges in oncology [2]. As complete as their review is, I would like to draw attention to another drug delivery system that is closely related to the topic where a prodrug, in this case ifosfamide, is converted in the peritoneal cavity by encapsulated cells expressing a P450 enzyme, CYP2B1. This converts ifosfamide in its active compound, 4-hydoxy-ifosfamide, that spontaneously decays to phosphoramide mustard and acrolein which alkylate DNA and protein, respectively. Using the standard model with GFP-expressing colon cancer cells as detailed in the excellent review [1] and also used by us with classical drug eluting beads[3, 4], we could demonstrate with the CYP2B1 encapsulated cells a significant tumor response all the way to complete remissions by using this gene directed enzyme prodrug therapy approach [5]. This concept, successfully proven in clinical studies in pancreatic cancer [6], could not be further developed due to manufacturing issues. Those, however, are resolved and further preclinical research in peritoneal carcinomatosis is ongoing.