High Ki-67 as an independent prognostic factor in extraskeletal osteosarcoma: a comparative cohort study.

BACKGROUND

The objectives of this study are to compare clinicopathological features and outcomes of extraskeletal osteosarcoma (EOS) and conventional osteosarcoma (COS) and identify independent prognostic factors for disease-free survival (DFS) and overall survival (OS).

METHODS

This study included 72 patients (Group EOS, n = 12; Group COS, n = 60) with a definitive diagnosis. Clinicopathological variables, SATB2 expression, and Ki-67 proliferation index were compared between groups. Outcomes were assessed using the Kaplan-Meier method and the log-rank test, and independent prognostic factors were identified by Cox regression analysis.

RESULTS

Group EOS had significantly higher median age (53.5 vs. 33.4 years, p < 0.001) and Ki-67 proliferation index than Group COS. Primary tumor location differed significantly (p < 0.001), with EOS cases affecting internal organs (kidneys, lungs) and COS cases mainly in long bones around the knee. Metastases were more common in Group EOS (83.3% vs. 13.6%, p < 0.001). Median OS and DFS for Group EOS were 19.3 months (vs. 71.6 months for COS, p = 0.007) and 2.2 months (vs. 21.6 months for COS, p < 0.001), respectively. Multivariate analysis identified age (OS: HR per year 1.04, 95% CI: 1.02-1.06, p < 0.001; DFS: HR 1.03, 95% CI: 1.02-1.05, p < 0.001) and Ki-67 proliferation index (OS: HR per %-point 1.02, 95% CI: 1.00-1.04, p = 0.038; DFS: HR 1.02, 95% CI: 1.01-1.04, p = 0.006) as independent prognostic factors.

CONCLUSIONS

Survival outcomes for patients with EOS were significantly worse than for those with COS. High Ki-67 proliferation index and advanced age were associated with a more aggressive clinical course of EOS. Therefore, more intensive follow-up and treatment are prudent for elderly EOS patients with a high Ki-67 proliferation index.