Experimental modeling of soft tissue sarcomas with invasion into bone structures.

Abstract

e23541 Background: This study aimed to establish and characterize PDX models of STS with bone invasion, evaluating their growth kinetics and verifying histologic fidelity to the primary patient tumors. Methods: The development of an orthotopic STS model with bone invasion was accomplished using two methods. To create an orthotopic PDX model of sarcoma with bone invasion, a fragment of a human tumor was implanted into the femoral bone of Balb/c Nude mice. For this purpose, the distal part of the mouse limb was preliminarily amputated to create a bed for the graft. The tumor material was fixed within the bone bed using a suture. The orthotopic PDX model of STS with invasion into a flat bone was created by implanting human tumor material into a surgically created defect in the pubic bone of immunodeficient Balb/c Nude mice under general anesthesia. Tumor nodule dimensions were measured weekly using a caliper, starting from day 7 post-implantation, over a period of 4 months with a frequency of twice per week. For histological examination, tumor nodules were fixed in 10% neutral buffered formalin for 24 hours, followed by the preparation of paraffin blocks. Results: Tumor samples from 13 patients with confirmed bone invasion were used to create two PDX models. A technique for orthotopic implantation into both long (tubular) and flat bones was established and optimized in Balb/c Nude mice. By day 35 post-implantation, invasion into long bones was confirmed in 12 out of 13 models, and into flat bones in 7 models. To verify stable growth and increase the biomass of tumor material, a second passage of the tumors was performed. This second passage yielded 6 stable xenografts with invasion into long bone and 3 with invasion into flat bone. Histological analysis revealed a predominance of pleomorphic undifferentiated sarcomas (50% of models). All xenografts retained the histological characteristics and infiltrative growth pattern of the original patient tumors. The successful engraftment rate of the orthotopic xenografts demonstrated a dependence on the bone tissue type. For long bones, characterized by richer vascularization and a specific microenvironment, the engraftment rate was 46.2% (6 out of 13), which is twice the result for flat bones (23.1%; 3 out of 13). The stable exponential growth of the six second-passage PDX models indicates successful adaptation of the xenografts to the long bone microenvironment. The range of final volumes (100.8–170.4 mm³) and the significant variability in growth rates (CV=22.4%) reflect the inherent biological heterogeneity of sarcomas. Conclusions: The obtained data demonstrate that the enhanced vascularization and unique microenvironment of long bones are critical for adequate tumor sustenance and for faithfully recapitulating the process of bone invasion in the established model.