An association between successful engraftment of osteosarcoma patient-derived xenografts and clinicopathological findings.

Although osteosarcoma is a rare disease, with a global incidence rate estimated at 5.0/million/year, it is the most frequent primary bone sarcoma in children and adolescents. In translational research, the patient-derived xenograft (PDX) model is considered an authentic in vivo model for several types of cancer, as tumorgrafts faithfully retain the biological characteristics of the primary tumors. Our goal was to investigate the association between PDX formation and clinical findings of osteosarcoma patients and the ability of the model to preserve in immunocompromized mice the characteristics of the parental tumor. A fresh sample of the patient tumor obtained from a representative biopsy or from surgical resection was implanted into nude mice. When tumor outgrowths reached ~1,500mm³, fresh PDX fragments were re-transplanted into new hosts. Engraftment in mice was obtained after a latency period of 19-225 days (median 92 days) in 40.54% of the implanted samples. We confirmed the histopathological fidelity between the patient tumor and their respective established PDXs, including the expression of biomarkers. PDX take rate was higher in surgical resection samples, in post-chemotherapy surgical samples and in samples from patients with metastatic disease at presentation. In conclusion, we have shown that the osteosarcoma PDX model reliably recapitulates the morphological aspects of the human disease after serial passage in mice. The observation that more aggressive forms of osteosarcoma, including those with metastatic disease at presentation, have a higher efficiency to generate PDXs provides a promising scenario to address several unanswered issues in clinical oncology.