(P 26) DEVELOPING AN ORTHOTOPIC MODEL OF DESMOPLASTIC SMALL ROUND CELL TUMOR

Objective: Desmoplastic Small Round Cell Tumor (DSRCT) is a rare and aggressive sarcoma of adolescent and young adults, characterized by high metastatic rates and poor prognosis. Current DSRCT patient-derived xenograft (PDX) models often exhibit slow growth and variable engraftment when implanted subcutaneously. Additionally, flank heterotopic models do not recapitulate the native DSRCT microenvironment since these tumors predominantly arise in the abdominal cavity. To address the need for in vivo DSRCT models with more consistent growth kinetics that better resemble the original tumors, we evaluated the impact of orthotopic (intraperitoneal) modeling of DSRCT on tumor engraftment and growth relative to heterotopic (subcutaneous flank) implantation.

Methods: DSRCT BER cells were transduced with a lentiviral vector for stable expression of mCherry and luciferase, enabling selection of transduced cells and subsequent in vivo tumor monitoring. NSG mice were divided into two groups for intraperitoneal and subcutaneous flank injections, and tumor growth was monitored weekly via bioluminescence imaging. Formalin-fixed paraffin-embedded (FFPE) samples from primary tumors and metastatic sites were collected at tumor endpoints for histology and immunohistochemical (IHC) analyses.

Results: Our optimized transduction protocol enabled the establishment of an orthotopic DSRCT CDX model. Following injection of mCherry-luciferase-labeled BER DSRCT cells, engraftment was uniformly confirmed by week 2 in 6 out of 6 mice for both groups, followed by overlapping tumor growth rates with no statistically significant differences. Metastases were observed in 4 out of 6 mice from the orthotopic group, with lesions in the spleen, omentum, abdominal wall, visceral fat, and rectum, whereas no metastatic spread was detected in the heterotopic group.

Conclusion: Our study provides proof of concept that orthotopic DSRCT models can be successfully generated and will be applied to patient-derived DSRCT models in upcoming work. Our development of a DSRCT model that better recapitulates the clinical behavior of DSRCT and its key molecular features provides an important model system for improved preclinical evaluation of existing and emerging therapeutic strategies.