Introduction

Peritoneal sarcomatosis (PS) in rhabdomyosarcoma (RMS) is a rare and the most advanced tumor stage with wide intraperitoneal tumor spread in children. Due to promising clinical reports, cytoreductive surgery (CRS) in combination with hyperthermic intraperitoneal chemotherapy (HIPEC) has been established as therapeutic option for PS . Nevertheless, this treatment is still experimental in children and not successful in all patients. The prognosis is sobering due to high probability of tumor recurrence . In a retrospective study on CRS and HIPEC (including seven cases of PS of RMS) the median over-all survival was 7.1 to 31.4 months after succeeded tumor resection whereas the diseases-free survival was described by 19.9 to 34 months depending on peritoneal cancer index (PCI). After incomplete cytoreductive surgery, no patient survived longer than 15 months . The evaluation of the intraperitoneal tumor spread and the achievement of complete CRS plays an integral role and might determine the therapeutic success . An enhancement of HIPEC by additive modalities such as photodynamic therapy (PDT) might be beneficial. The principle of PDT is a photosensitive agent, which ideally accumulates selectively in tumor cells. After illumination with light of the appropriate wavelength in the presence of oxygen the photoactivated sensitizer generates highly reactive oxygen species (ROS) leading to critical cytotoxicity and destruction of tumor cells via apoptosis or necrosis . Furthermore, photosensitizer are known to show fluorescence enabling visualization and focused resection of tumor tissue during photodynamic diagnosis (PDD) . The natural photosensitizer Hypericin (HYP), an extract from the St. John’s wort, represents an ideal and promising agent for the challenging treatment of PS of RMS: HYP with its strong self-fluorescence and low photobleaching has been used successfully as photosensitizer for in vitro and in vivo visualization and PDT of pediatric RMS . Up to now there are no data on combining HYP and HIPEC in RMS in vivo . Therefore, we tested a combination of the photosensitizer HYP with HIPEC in a recent established murine HIPEC animal model of intraperitoneal disseminated pediatric RMS.