We examined the effect of 15d-PGJ2 on the viability, migration, invasion, and secretion of PTHrP in MDA-MB-231 metastatic human breast cancer cells, RANKL and OPG expression in hFOB1.19 osteoblastic cells, RANKL-induced osteoclastogenesis in mouse bone marrow macrophages, and bone resorption by mature osteoclasts. The gene discussed is PTHLH; the disease is breast carcinoma.