[Bone tissue and cancer].

Bone remodeling is a constant phenomenon balancing between osteoblastic bone formation and osteoclastic bone resorption in the neighbourhood of a cellular micro-environment including stromal and hemopoietic cells. Numerous local factors and hormones modulate such a mechanism and act synergistically, usually through the indirect production of osteoblastic coupling factors. The majority of the cytokines acting on bone remodeling possess both actions upon activation of mature osteoclasts and differentiation of hemopoietic osteoclast progenitors. Components from bone matrix which include non-collagenous bone proteins and other local factors are major products acting on bone remodeling. The presence of a cancer may determine changes in bone remodeling, directly through tumor-mediated resorption or indirectly through the action of local or systemic factors with or without tumor involvement of bone. Bone remodeling associated with cancer is usually an uncoupled phenomenon with decreased bone formation and increased bone resorption. In B-cell malignancies, abnormal bone remodeling is an early event linked to specific bone involvement. Abnormal osteoclast differentiation (micro- or macro-resorption) represents a major difference between myeloma and other B-cell malignancies. Several synergistic factors produced by tumor cells and micro-environment are usually implicated in the pathogenesis of bone lytic lesions, hypercalcemia or histomorphometric bone changes associated with cancers.