Histopathological observations on osteolytic bone metastasis

Abstract

Three types of bone metastasis can be identified : the osteolytic, osteoblastic and the intertrabecular metastasis. Bone resorption is believed to be responsible for osteolytic metastasis. The early stage of metastatic lesion showed tumor cells loosely intermingled with osteoblasts, fibroblastic stromal cells, osteoclasts and endothelial cells. In the metastatic nest, many tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts accumulated in direct contact with alkaline phosphatase (ALP)--or receptor activator of NF-kappaB ligand (RANKL)-positive osteoblastic cells, indicating the osteoclastogenesis. On the other hand, osteoclasts express CD44 while osteopontin was abundant in the stromal tissue of tumor nests. Therefore, mediating its affinity for CD44, osteopontin may serve to facilitate osteoclastic migration. We review the histopathological microenvironment featuring osteoclastic bone resorption, angiogenesis and matrix degradation, which appears to facilitate proliferation of tumor cells after the onset of bone metastasis.