Human breast cancer induces osteoclast activation and increases the number of osteoclasts at sites of tumor osteolysis.

The cellular mechanism through which osseous breast cancer metastases induce the focal destruction of bone (tumor osteolysis) is unknown. An athymic mouse model designed for the study of tumor osteolysis was developed and the influence of two human breast cancer tumors on bone was studied. Tumor-induced osteolysis occurred between 7 and 10 weeks after inoculation of mouse femora with MDA-MB-231 or MDA-MB-435s breast cancer cells.