[Biology of osteoclasts; their role in bone metastases]

Bone is a common site for metastasis of malignant tumors. These can be recognized radiologically as either lytic or sclerotic lesions since the tumor cells stimulate resident bone cells to cause excessive local resorption or new bone formation. The osteoclast, as the only cell being capable of resorbing bone, is of major importance for the homing of tumor cells in bone and progression of metastasis due to bone destruction. Thus, the improvement of our means of therapeutic intervention towards prevention of tumor progression and pathological fractures will depend on our better understanding of both the molecular basis of bone resorption and the cellbiology of the osteoclast. This article presents our current opinion of the molecular mechanisms of bone resorption by the osteoclast. After describing the morphological features of the osteoclast, aspects such as cell mobility, attachment, enzymes synthesis, transmembrane transport, osteoclast differentiation and function, as well as the protooncogenes c-src and c-cbl and their role in bone resorption are presented in detail.