113P Real-world data from patients with osteosarcoma treated in 4 medical centers in Greece: Ninety percent or greater tumor necrosis is associated with disease-free survival

Osteosarcoma (OST) is the most frequent primary bone cancer, mainly affecting patients of younger age. Although surgery combined with cytotoxic chemotherapy has significantly increased the chances of cure, recurrent and refractory diseases still impose a tough therapeutic challenge. Advanced OSTs tend to have a poor prognosis with limited therapeutic options beyond first-line therapy. Herein, we report real-world data obtained from cancer registries in Greece. We retrospectively studied the predictive value of distant metastasis, percentage of necrosis, and grade of tumor in 77 cases of sarcoma treated in 4 medical centers in Greece between 2004 and 2022. Demographic characteristics and survival data are also reported in this study. The median follow-up time from the time of diagnosis was 27 months. Initial analysis of the data revealed that short bones were affected significantly more frequently in older (median age 43 (30, 50)) than younger patients (median age 26 (18, 40)). 10 (18%) patients had distant metastasis at the time of diagnosis and 39 (81%) had grade 3 disease. Distant metastasis was significantly associated with shorter overall survival (OS; HR 3.7, p=0.01). In addition, we investigated the association of tumor necrosis with DFS and OS and we found that tumor necrosis 90% or greater was significantly associated with longer DFS (HR 0.09, p=0.003) but not with OS (HR 0.62, p=0.3). The grade of tumor or bone affected (long vs short) had no significant correlation with survival. We present real-world data from OST patients treated in 4 tertiary medical centers in Greece. As previously reported, we found a survival advantage for patients with 90% tumor necrosis. Future studies should examine potential drivers of this important finding, such as a delay in presentation or deviation from standard of care practices.