The skeleton as a unique environment for breast cancer cells.

Bone is a favored location for several cancer metastases especially breast, prostate and myeloma. This review evaluates various properties of the skeleton that contribute to its successful colonization by breast cancer cells. The first consideration is the unique aspects of the vasculature of metaphyseal bone, which may account for the initial lodging of breast cancer cells in specific regions of the skeleton. Metasphyseal bone, found at the ends of long bone, in ribs and in vertebrae, is comprised of trabecular bone interspersed with marrow and a rich vasculature. The chemotactic factors that arise from bone marrow and bone cells are discussed in terms of cancer cell migration out of the vasculature and entry of cancer cells into the marrow cavity. Once the breast cancer cells have migrated into the metaphysis, they interact both directly and indirectly with bone cells and other cells in the marrow. As tumor growth progresses, functional bone cells are lost, most likely through apoptosis.