The prognostic value of pretreatment complete blood count parameters in primary osteosarcoma: a multicenter study of 449 patients receiving neoadjuvant therapy

Neoadjuvant chemotherapy has improved survival rates in osteosarcoma patients. However, reliable pretreatment prognostic markers for predicting treatment outcomes remain limited and underexplored. In this multicenter retrospective study, 308 osteosarcoma patients from ZJU hospital (training cohort) and 141 patients from RJ hospital (testing cohort) who underwent neoadjuvant chemotherapy followed by tumor resection were analyzed. Tumor necrosis rates, complete blood count (CBC) parameters, and various clinical features were evaluated. The training cohort was used to develop a predictive model, which was subsequently validated in the testing cohort. Prognostic factors were evaluated using Chi-square, Mann–Whitney U, Cox regression, and log-rank tests. Most tumors (95.5%) were in the extremities and the majority (86.4%) were classified as Enneking stage II. Pretreatment metastasis was observed in 12.0% of patients and emerged as an independent adverse factor for both OS and PFS. Lower pretreatment monocyte percentage (MO%) was significantly associated with favorable chemotherapy response and higher overall survival (OS) rates in both cohorts. Elevated MO% (≥ 8%) was identified as an independent predictor of poorer OS in multivariate analysis. For progression-free survival (PFS), elevated MO% was associated with worse outcomes in the testing cohort, suggesting its potential role in predicting tumor progression, although this association did not reach statistical significance in the training cohort. Pretreatment MO% is a simple and readily accessible biomarker that independently predicts OS in osteosarcoma patients. Lower MO% correlates with improved chemotherapy response and survival outcomes, whereas elevated MO% and pretreatment metastasis indicate higher risks. Incorporating MO% into pretreatment evaluation may enable early risk stratification and guide personalized treatment strategies in osteosarcoma management. However, its predictive value for PFS remains exploratory and requires further validation in larger prospective studies.