The ribs, pelvis and spine are normally the first bones involved and distal bones are rarely affected. Metastases are established when a single tumor cell or a clump of cells gain access to the blood stream, reach the bone marrow through blood vessels in Haversian canals, extravasate, multiply and neovascularize. Batson's vertebral venous plexus allows cells to enter the vertebral circulation without first passing through the lungs. The sluggish blood flow in this plexus is more conducive to tumor survival, accounting for the high rate of prostate cancer metastasis to the spine. Pain, pathological fractures and hypercalcemia are the major sources of morbidity with bone metastasis.
Pathological fractures are most common in breast cancer due to the lytic nature of the lesions.
They are uncommon in lung cancer due to short life span and rare in prostate cancer which tend to be osteoblastic lesions. It is also difficult to distinguish between metastases and benign lesions such as Paget's disease or osteoporosis on plain film. On bone scan, radiolabeled bisphosphonates are taken up by in areas of bone formation but not by the tumor cells. CT is more specific than bone scan and can distinguish between osteolytic and osteoblastic lesions. MRI is the most sensitive method of detection bone metastases because cells can spotted before local bone reaction has occurred.