SPP1 and breast cancer: Another study by Kang et al. indicated that over-expression of CTGF alone in human breast cancer MDA-MB-231 cells did not cause a significant increase in bone metastasis formation, whereas over-expression of CTGF together with interleukin-11 (IL-11) and osteopontin (OPN) showed a dramatic increase both in the rate and in the incidence of bone metastases [47].