RUNX2 and breast carcinoma: Next, we stained the tibia of mice injected with an admix of MDA-MB-231GFP/Luc2 human breast cancer cells plus MC3T3-E1 murine osteoblasts using antibodies for FOXN1, to show the population of injected MC3T3-E1 cells, and RUNX2 a unique marker of osteoblasts [64].