Evaluation of the Prognostic and Therapeutic Factors Affecting Outcomes in Parosteal Osteosarcoma of Bone.

Abstract

The goal in treating parosteal osteosarcoma is to achieve wide margins while minimizing morbidity. Marginal resections increase local recurrence (LR) risk. The impact of intramedullary involvement on outcomes remains unclear. We examined the role of quantitative margins and the effect of intramedullary involvement  on LR  and outcomes. We performed a retrospective analysis of 42 surgically treated parosteal osteosarcoma cases over 20 years (2000-2020) at a tertiary cancer centre. Final histopathology confirmed low-grade tumors in 39 cases and dedifferentiated in 3. Of 39 patients, 2 had amputations and 37 underwent limb salvage. Eight needed intra-operative vascular reconstruction. Quantitative margins were assessed in 25 primary cases with adequate follow-up: 10 had margins < 2 mm, 15 had ≥ 2 mm; 15 had margins < 5 mm, 10 had ≥ 5 mm. Among 37 patients with follow-up, 31 are alive and disease-free (22 continuously disease-free), while 6 have died (5 due to disease, 1 cardiac event). Median follow-up was 108 months (range 27-273). Ten patients had LR. Margins of ≤ 2 mm versus > 2 mm did not significantly influence outcomes, indicating that simply exceeding 2 mm was not associated with improved local control. However, a critical threshold effect was observed at ≥ 5 mm, as no patients with margins ≥ 5 mm developed local recurrence (LR). Three had isolated LR, seven combined relapses (LR + distant). Of these ten, five are alive and disease-free, four died of disease, one died of cardiac event. Intramedullary involvement did not affect LR (p = 0.69) but had a trend towards poor disease specific survival (DSS). The above findings underscore that achieving margins ≥ 5 mm represents a clinically meaningful cutoff, beyond which the risk of local or combined relapse is minimized, supporting ≥ 5 mm as the optimal target for oncologic resection margins. Intramedullary involvement and LR have a trend towards poor DSS.