definition- tumours of the musculo-skeletal system can either be benign or malignant, primary, secondary and are best understood if discussed in terms of their origin. benign tumours progress slowly, not invasive and do not metastasise, while malignant tumours grow fast, invasive and they metastasise. primary tumours arise from bone and produce bone cell, while secondary tumours are as a result of metastasis and need not contain the host cells.