Gord Zhu

Objectives Distinguishing enchondromas (grade 0) from grade 1 chondrosarcomas, recently classified as atypical cartilaginous tumors (ACT), is challenging due to histologic and radiographic similarity. However, diagnostic ambiguity poses a management dilemma: enchondromas are observed, while ACTs are excised. Protein Ki-67 is a cellular proliferation nuclear marker used as a proxy for aggressiveness in other tumors. This retrospective pilot study aimed to characterize the association between grade and Ki-67 index and evaluate its ability to aid differentiation between critical cartilage tumor grades. Methods Tissue blocks from 26 patients treated for enchondromas or chondrosarcomas within the past ten years were exposed to anti-Ki-67 rabbit monoclonal antibody and hematoxylin counterstain. Counting two high-power fields per sample yielded a Ki-67 index. Results There was a strong positive correlation between tumor grade and the Ki-67 index (r = 0.704, P<0.001). One-way analysis of variance (ANOVA) showed significant differences in the Ki-67 index between grades (P<0.001). Tukey’s post-hoc test demonstrated that enchondroma Ki-67 indexes were not significantly different from ACT Ki-67 indexes (P=0.094). Receiver operator curve cutoff index value of 13.4% differentiated enchondroma vs. ACT with 67.9% sensitivity and 42.9% specificity. Conclusion Ki-67 index is correlated with cartilage tumor grade. Although our study did not show a significant difference in the Ki-67 index between enchondromas from ACTs, this study provided a protocol for future investigations. Study limitations include small sample size and reliance on historical tissue blocks of variable preservation quality.