SPP1 and neoplasm: OPN expression was associated with higher percentage of Ki67-positive cells in clinical material (p = 0.012), while OPN blocking in α-SMA-positive CAF-derived CM attenuated growth of lumBC cell line colonies in 3D Matrigel.<h4>Conclusions</h4>Our findings demonstrate that α-SMA-positive CAFs might enhance tumor growth via secretion of OPN.