SPP1 and invasive carcinoma: Single-cell RNA sequencing (sc-RNA seq) on early invasive carcinoma MIC wild-type (WT) and β1 integrin-deficient tumors (dormant stage) revealed that the epithelial tumor cells expressed elevated levels of osteopontin (OPN, Spp1) (Fig. 1a), a secreted cytokine and ECM protein that has both tumor cell-autonomous and stromal targets.