In an in vitro system where a human breast cancer cell line and a mixture of mouse calvarial osteoblasts and bone marrow derived macrophages were co-cultured in the upper and lower chambers of a transwell, respectively, stimulation of PTX3 expression in the tumor cells by TNF-α enhanced Rankl expression and osteoclast formation in the lower compartment, suggesting a role for PTX3 in cancer-related osteolysis that however requires validation in vivo (57). This evidence concerns the gene PTX3 and breast cancer.