Several preclinical studies showed that metastatic breast cancer cells, directly [54,55,56,57,58,59] or through Jagged1-expressing tumor cells [58], induced osteoblasts to express high levels of IL-6 [54,55,56,57,58,59,60,61], while they seemed to not affect IL-6 production by osteoclasts [62,63]. The gene discussed is JAG1; the disease is breast carcinoma.