Introduction

The tumors that most frequently develop bone metastases are those from the breast, prostate, thyroid, lung, and kidney. The most common sites of bone metastases include vertebrae (70%), pelvis (40%), femur, and ribs.

Bone metastases are due to the hematogenous dissemination of neoplastic cells from the primary tumor. Metastatic cells settle in the bone marrow before affecting the cortex. Around those cells a release of factors takes place activating the osteoclasts and increasing bone resorption. As a reaction, the osteoblasts increase bone formation. Thus, lytic and blastic components coexist in bone metastases. X-ray imaging not only shows the tumor occupying bone volume, but a complex of neoplastic tissue and bone reaction both lytic and blastic.

Although many bone metastases are asymptomatic, the main clinical features (Table 60.1), where present, are usually localized pain, fractures, and collapses, with their functional (instability), neurological (spinal cord compression) or metabolic (hypercalcemia) complications. The alkaline phosphatase that indicates osteoblastic activity rises in 70% of the patients diagnosed with bone metastases. X-ray, computer-assisted tomography (CAT) and magnetic resonance imaging (MRI) show bone metastases as an increase or decrease of density in relation to the adjacent bone. Bone scintigraphy is more sensitive than conventional radiographs, and it shows the blastic activity around the metastases. MRI is even more sensitive and can be used to confirm early metastases shown by bone scan but not by conventional x-rays.

Bone metastases are not life threatening in themselves, but their presence means that there is a hematogenous tumor dissemination.