(P 17) EXTRASKELETAL OSTEOSARCOMA: MICRORNA PATTERNS PROVIDE INSIGHTS INTO SIMILARITIES AND CONTRASTS WITH OTHER SARCOMAS

Objective: Extraskeletal osteosarcoma (ESOSA) is a rare sarcoma histology. Despite its official classification as a soft tissue sarcoma, ESOSA shares similarities with conventional osteosarcoma (OSA), and the sarcoma literature lacks clear consensus on clinical treatment paradigms. Therefore, the objective of this study was to profile and compare the microRNA expression of tumor samples from patients with ESOSA, OSA, and common soft tissue sarcoma (STS) subtypes.

Methods: Final analysis included 33 tumor samples: 5 OSA, 12 ESOSA, and 16 STS. MicroRNA profiling was conducted using the MiRXES real-time RT-PCR assay (MiRXES, Singapore). Raw miRNA expression data underwent two-step normalization: global scaling to equalize sample means, followed by feature-wise Z-scoring to standardize miRNA expression distributions. Hierarchical clustering was performed using multiple linkage (ward, average, complete) and distance metrics (Euclidean, correlation, cosine). Chi-squared tests assessed associations between cluster assignments and tissue types. Statistical analysis included per-miRNA t-tests with FDR correction between tissue groups and calculation of three pairwise fold change ratios (OSA vs ESOSA, STS vs ESOSA, OSA vs STS).

Results: Preliminary analysis of average miRNA expression revealed a statistically significant difference between primary OSA and STS. In contrast, ESOSA samples did not exhibit materially different overall miRNA expression from STS, while they exhibited a trend for overall miRNA expression difference from primary OSA.

Conclusion: Our analysis to date suggests that ESOSA displays a miRNA expression pattern that appears to be closer to STS than to primary OSA. We also found that miRNA analysis can more clearly discriminate between primary OSA and STS, extending background knowledge about genomic differences between these histotypes. Comprehensive analysis is ongoing and will be presented at the conference. Our findings suggest that studies of larger cohorts are warranted to better elucidate the molecular similarities and differences between ESOSA, primary OSA, and STS.