Cancer and bone: A complex complex

• Cancer in bone is not curable by current therapies.
• Bone is a preferential site for metastases, mostly prostate and breast cancer cells.
• Metastatic cancer cells interact with the total bone micro-environment.
• Cancer cells change both bone resorption and formation to stimulate their own growth.
• Understanding the complex interaction of cancer and bone is crucial for new therapies.

Primary and secondary bone cancers are rare events. However, once settled, a complex process is started involving an extensive amount of factors and interactions. The bone micro-environment is a preferential site for (metastatic) tumor cells to enter, stay, colonize and expand. The fact that the tumor cells affect the complete bone environment involving many cell types and regulatory pathways to stimulate their own growth and escape from therapy is devastating for the patient. Many efforts have been made to get more insight into the mechanisms underlying the communication between bone cells and cancer cells and progress is made in therapeutic interventions. This review will discuss the biological mechanisms of primary bone malignancies (osteosarcoma, Ewing’s sarcoma, chondrosarcoma, multiple myeloma) and secondary bone malignancies (bone metastases) and therapeutic interventions.