SPP1 and cancer: Unexpectedly, we saw two distinct populations of osteoblasts based on protein marker expression in cancer-bearing bones: (1) orange arrows point to osteoblasts both OPN-positive (red) and aSMA-positive (yellow)—combined colors result in osteoblasts orange in color; (2) white arrows point to osteoblasts OPN-positive (red), but aSMA low (yellow)—combined colors result in osteoblasts red in color (Fig. 1a, inset).