SPP1 and central nervous system cancer: Distribution of OPN+ cells within gliomas displays a few small OPN+ cells (OPN-LI of 4.5 ± 1.8%) dispersed inside the proliferative mass in stage I, while OPN+ large cells in stages II and III (OPN-LI of 7.7 ± 0.8% and 12.3 ± 1.2%, respectively) predominate on the border.