SPP1 and cancer: To determine the main source of OPN in vivo and validate STAT3-dependency, we analysed OPN gene expression across MAFs (GFP+), cancer cells (Epcam+), immune cells (CD45+), isolated by flow cytometry-based cell sorting from metastasis bearing Pdgfrb-GFP mice treated with STAT3i (Fig. 7F and Supplementary Fig. 7J).