Diagnostic challenges in low-grade central osteosarcoma

Low-grade central osteosarcoma (LGCOS), a rare type of osteosarcoma, often has misleading radiological and pathological features that overlap with those of other bone tumours, thereby complicating diagnosis and treatment. We aimed to analyze the clinical, radiological, and pathological features of patients with LGCOS, with a focus on diagnosis, treatment, and outcomes.

We retrospectively analyzed the medical records of 49 patients with LGCOS (Broder's grade 1 to 2) treated between January 1985 and December 2017 in a single institute. We examined the presence of malignant features on imaging (periosteal reaction, cortical destruction, soft-tissue invasion), the diagnostic accuracy of biopsy, surgical treatment, and oncological outcome.

Based on imaging, 35 of 49 patients (71.4%) exhibited malignant features. Overall, 40 of 49 patients (81.6%) had undergone a biopsy before en-bloc resection: 27 of 40 patients (67.5%) were diagnosed on the first biopsy, which was more accurate when carried out by open rather than needle biopsy (91.3% vs 35.3% diagnostic accuracy, respectively; p < 0.001). Of the 40 patients treated by en-bloc resection, surgical margins were wide in 38 (95.0%) and marginal in two (5.0%). Furthermore, nine of 49 patients (18.4%) underwent curettage (intralesional margin) without previous biopsy. All patients with a positive margin developed local recurrence. Distant metastases occurred in five of 49 patients (10.2%). The mean five-year overall survival (OS) and distant relapse-free survival (D-RFS) were 89.3% (SD 5.1%) and 85.7% (SD 5.5%), respectively. Univariate analysis showed that the occurrence of distant metastasis was a poor prognostic factor for OS (hazard ratio 11.54, 95% confidence interval (CI) 1.92 to 69.17; p < 0.001). Local recurrence was a poor prognostic factor for D-RFS (HR 8.72, 95% CI 1.69 to 45.0; p = 0.002).

The diagnosis of LGCOS can be challenging because it may present with non-malignant features and has a low diagnostic accuracy on biopsy. If precisely diagnosed, LGCOS can be successfully treated by surgical excision with wide margins.