Bone Metastases

Abstract

Metastases represent the most common bone tumor and outnumber primary bone tumors 20-to-1. Moreover, bone metastases have an extremely varied imaging appearance and are difficult to exclude from many differentials. This is especially true in patients over 40 years of age and in those with a known primary malignancy. Metastatic lesions develop when cells from the primary tumor separate and travel to distant sites, where they adhere and grow. Most often, malignant cells spread hematogenously, but they can also spread via the lymphatic system or by direct extension. The cells must be able to (1) survive the transit from the primary site and (2) once at the secondary site, develop their own blood supply, in order to grow. Thus, the vast majority of bone metastases occur in the spine and pelvis, where there is richly vascularized red marrow. Conversely, metastases are rarely found in the bones of the hands and feet, as these areas are filled with fatty marrow. Besides a rich blood supply, several growth factors are produced or stimulated by the tumor in order to optimize its establishment, survival, and growth at the secondary site.