Comparison of bone mineral density between the tumour side and the healthy side in patients with malignant tumours of the long bones of the lower extremities: a prospective study

This study aimed to compare bone mineral density (BMD) between the tumour-affected and contralateral healthy sides in patients with primary or metastatic malignant tumours of the long bones of the lower extremities, and to evaluate the clinical relevance of these differences regarding fracture risk. A single-centre, prospective observational study was conducted at Uludağ University between May 2021 and May 2022. Forty-two patients (22 with primary and 20 with metastatic malignant tumours of the femur or tibia) were included. Bilateral BMD measurements were obtained using dual-energy X-ray absorptiometry (DEXA). Demographic data, biochemical parameters (vitamin D, parathyroid hormone [PTH], calcium), and tumour characteristics were recorded. Inter-side BMD differences were analysed, and correlations with clinical and biochemical factors were assessed using Spearman correlation and multiple linear regression analyses. Patients with metastatic tumours were significantly older (median 67.5 years) than those with primary tumours (median 46 years, p = 0.002). Lumbar and tumour-side DEXA values were significantly lower in the metastasis group (p = 0.035). Intra-group analyses revealed that BMD on the tumour side was significantly reduced compared with the contralateral side in both groups (p < 0.001), indicating a marked local bone loss. Correlation analysis showed a negative association between age and DEXA scores in metastatic cases, while BMI correlated positively with lumbar BMD. PTH level emerged as a significant independent predictor of BMD across all regression models (p < 0.01). Malignant tumours of the lower-extremity long bones lead to a significant reduction in local BMD, independent of systemic bone metabolism. The results highlight the importance of bilateral DEXA evaluation to differentiate local from systemic bone loss and to better predict fracture risk. Routine assessment of PTH may further assist in monitoring bone health in oncologic patients.