Lipid Metabolic Reprogramming and Epigenetic Co-Dysregulation Across the Central Chondrosarcoma Grade Spectrum: A Multi-Cohort RNA-seq Study

Central chondrosarcoma is the second most common primary malignant bone tumour, and grade progression markedly worsens prognosis. The contributions of lipid metabolic reprogramming and epigenetic co-dysregulation to grade progression remain poorly characterised. We integrated a bulk RNA-seq discovery cohort of 53 graded central chondrosarcomas (GSE299759) with a single-cell analysis of eight chondrosarcomas (GSE184118). Because the atypical cartilaginous tumour (ACT) and dedifferentiated groups each comprised only three samples, the Grade 3 versus Grade 2 contrast was pre-specified as the primary comparison. Curated panels of 44 lipid metabolism genes and 50 epigenetic regulators were assessed by differential expression and a correlation-based connectivity ranking, evaluated by permutation testing. In the primary Grade 3 versus Grade 2 comparison, SQLE, ACACA, and FASN were upregulated (FDR < 0.05), indicating a grade-associated increase in de novo lipogenesis. In the exploratory Grade 3 versus ACT comparison, additional lipid genes (HMGCR, LDLRAP1) and the epigenetic regulators EHMT2 and SIRT2 showed altered expression, although the small ACT group limits these estimates. A connectivity ranking highlighted FASN, KMT2C, TET2, SETD5, and KDM5B; permutation testing confirmed this co-expression structure was non-random (p < 0.0001). Single-cell analysis showed FASN, SETD5, and KDM5B are expressed predominantly in malignant cells, whereas KMT2C and TET2 are not, indicating cell-type heterogeneity. De novo lipogenesis upregulation is the most consistent lipid alteration in high-grade central chondrosarcoma, nominating SQLE, ACACA, and FASN as candidates for experimental investigation.