Tumor Immune Microenvironment–Associated Prognostic and Mifamurtide-Response Gene Signatures for Localized Osteosarcoma: A Correlative Study of the ISG/OS-2 Trial

Abstract Purpose: A risk-adapted treatment strategy, the ISG/OS-2 trial, evaluated the use of mifamurtide in patients with P-glycoprotein (Pgp)–positive localized osteosarcoma. The primary objective was the identification of prognostic classifiers based on tumor microenvironment (TME) gene profiling in all patients and in those undergoing mifamurtide treatment. Experimental Design: RNA from pretreatment formalin-fixed, paraffin-embedded nondecalcified tissues of 62 patients was analyzed with the PanCancer Immune Profiling Panel (NanoString Technologies). Thirty-three (53%) of 62 Pgp-positive patients underwent chemotherapy + mifamurtide; 29 (47%) of 62 Pgp-negative patients received chemotherapy alone. Univariate Cox regression, ROC curve, and CIBERSORTx algorithm gene deconvolution analyses were performed. Results: A 21-gene signature able to stratify all patients into high risk (Hi-R) and low risk (Lo-R) was identified: 5-year overall survival (OS) of 47% for Hi-R and 92% for Lo-R (P = 3e−06). TME of Lo-R compared with Hi-R was significantly enriched in CD8 T cells, regulatory T cells, and NK-activated cells and diminished in CD4 T cells. The 21-gene signature was validated in two independent sets: TARGET-OS The Cancer Genome Atlas (n = 62) and GSE33382 (n = 57). For patients treated with chemotherapy + mifamurtide, 31 mifamurtide-related genes able to distinguish Hi-R and Lo-R in terms of OS (P = 1e−09) and event-free survival (P = 3e−06) were also identified. After multivariate analysis, the 21- and 31-gene mifamurtide-related signatures were independently associated with OS (P = 0.00044 and P = 0.000079, respectively). 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.