Prognostic value of patient-derived xenograft engraftment in pediatric sarcomas

Abstract

The goals of this work were to identify factors favoring patient-derived xenograft (PDX) engraftment and study the association between PDX engraftment and prognosis in pediatric patients with Ewing sarcoma, osteosarcoma, and rhabdomyosarcoma. We used immunodeficient mice to establish 30 subcutaneous PDX from patient tumor biopsies, with a successful engraftment rate of 44%. Age greater than 12 years and relapsed disease were patient factors associated with higher engraftment rate. Tumor type and biopsy location did not associate with engraftment. PDX models retained histology markers and most chromosomal aberrations of patient samples during successive passages in mice. Model treatment with irinotecan resulted in significant activity in 20 of the PDXs and replicated the response of rhabdomyosarcoma patients. Successive generations of PDXs responded similarly to irinotecan, demonstrating functional stability of these models. Importantly, out of 68 tumor samples from 51 patients with a median follow-up of 21.2 months, PDX engraftment from newly diagnosed patients was a prognostic factor significantly associated with poor outcome (p = 0.040). This association was not significant for relapsed patients. In the subgroup of patients with newly diagnosed Ewing sarcoma classified as standard risk, we found higher risk of relapse or refractory disease associated with those samples that produced stable PDX models (p = 0.0357). Overall, our study shows that PDX engraftment predicts worse outcome in newly diagnosed pediatric sarcoma patients.

Keywords: Ewing sarcoma; osteosarcoma; patient-derived xenograft; prognosis; rhabdomyosarcoma.

Figure 1

Comparative histology (hematoxylin and eosin and IHC staining) of six representative cases of original human tumor biopsies and the corresponding PDXs at early passages (F0/F2) and late passage (F5). CD99 (cell membrane), SPARC (cytoplasm), and MyoD1 (nuclear) are stained in brown. These representative samples were selected from six Ewing sarcomas, three osteosarcomas, and three rhabdomyosarcomas with complete histopathology studies. All images were obtained using a microscope at ×40 objective magnification. Scale bar represents 50 μm.

Figure 2

Antitumor activity of irinotecan in subcutaneous PDX. (A) Change in tumor volume (mean and STDEV of 3–15 tumors) at the end of irinotecan treatment (day 14). (B) Percentage of tumor models achieving each response. (C) Tumor volume (% of volume at treatment start) in three PDX pairs at passage F ≤ 2 or F ≥ 6, treated with one cycle of irinotecan (treatment) or not treated (control). Models and F were HSJD‐ES‐009 (F2 versus F6), HSJD‐ES‐017 (F1 versus F8) and HSJD‐aRMS‐2 (F2 versus F10).

Figure 3

Kaplan–Meier estimation of (A) EFS and (B) OS among all patients with positive (n = 30) or negative (n = 38) engraftment of their PDX.

Figure 4

Kaplan–Meier estimation of (A) EFS and (B) OS among patients of the diagnostic cohort with positive (n = 7) or negative (n = 24) engraftment of their PDX.

Figure 5

Kaplan–Meier estimation of (A) EFS and (B) OS among patients of the relapse cohort with positive (n = 23) or negative (n = 14) engraftment of their PDX.