Real-time PCR analysis indicated that RANKL mRNA levels increased considerably and OPG mRNA levels decreased noticeably in osteoblastic hFOB1.19 cells stimulated with 75% CM from MDA-MB-231 breast cancer cells or PTHrP (100 nM) for 6 h, which elevated the RANKL/OPG ratio. This evidence concerns the gene TNFRSF11B and breast cancer.