Osteopontin was observed in the tumor-bearing bones of mice injected with MDA-MB-231GFP/Luc2 cells plus EO-231 cells (~ 35% of cells); however, no osteopontin expression was found in the tumor of mice injected with MDA-MB-231GFP/Luc2 cells plus MC3T3-E1 cells (0% of cells) (Additional file 6: Figure S6). The gene discussed is SPP1; the disease is neoplasm.