Tumor immune microenvironment-associated prognostic and mifamurtide-response gene signatures for localized osteosarcoma: a correlative study of the ISG/OS2 trial

A risk-adapted treatment strategy, the ISG/OS-2 trial, evaluated the use of mifamurtide in P-glycoprotein (Pgp)-positive localized osteosarcoma patients. Primary objective was the identification of tumor immune microenvironment (TME) prognostic classifiers in all patients and in those undergoing mifamurtide. RNA from pre-treatment FFPE non-decalcified tissues of 62 patients was analyzed with the PanCancer Immune profiling panel.Thirty three out of sixty-two (53%) Pgp-positive patients underwent chemotherapy (CT) + mifamurtide, 29/62 (47%) Pgp-negative patients received CT alone. Univariate Cox regression, ROC curve and CIBERSORTx algorithm gene deconvolution analyses were performed. A 21-gene signature able to stratify all patients into high-(Hi-R) and low-risk (Lo-R) was identified. TME of Lo-R vs Hi-R, was significantly enriched in T-regs, CD8 T-cells and NK activated cells, and diminished in CD4 T-cells. The 21-gene signature was validated in two independent sets. For patients treated with CT+mifamurtide a 31-gene mifamurtide-related signature able to distinguish Hi-R and Lo-R in terms of OS and EFS was also identified. In conclusions a validated osteosarcoma TME prognostic gene signature has been identified, regardless of mifamurtide treatment. Importantly, a mifamurtide-related signature was also developed. Tumor-immune interactions possibly implicated in disease progression and treatment response were shown. This is a retrospective, translational study on 62 patients with high-grade osteosarcoma. Inclusion criteria were a diagnosis of localized primary high-grade osteosarcoma included in the ISG-OS2 trial and treated with chemotherapy or chemotherapy and adjuvant mifamurtide. Among these, 33/62 patients (53%) were Pgp-positive and received chemotherapy plus adjuvant mifamurtide, while the 29/62 (47%) Pgp-negative patients underwent chemotherapy alone.