Although rare among the general population, bone malignancies have a high rate of incidence among children and adolescents and are associated with high mortality rates. Osteosarcoma (also known as osteogenic sarcoma) is the most frequent primary cancer of bone and shows a high tendency to metastasize to the lung. Despite the frequent use of osteosarcoma-derived cell lines in basic biomechanical research and for the evaluation of cell responses to new biomaterials, the mechanical phenotype and the differences between osteosarcoma cells and related cell types, such as mesenchymal cells, osteoblasts and osteocytes, remain largely unknown. In the present review we summarize current knowledge of the biophysical and mechanical properties of the niche of primary osteosarcomas and of the malignant cells, and discuss the impact of these features on the progression of malignancy.