SPP1 and cancer: Desialylation may enhance BSP’s affinity for COL and, consequently, increase cancer cell adhesion the bone matrix.41 Hypophosphorylated or unphosphorylated Thr residues may promote cancer cell adhesion,42 as evidenced by increased adhesion of MDA-MB-435 melanoma cells to low-phosphorylated OPN relative to highly phosphorylated OPN.151 This may reflect altered integrin affinity (αvβ3 or αvβ5),152 affecting RGD-integrin interactions.