SPP1 and lung cancer: Upregulation of OPN expression contributed to cisplatin (DDP) resistance in cervical cancer cells [67,68], cetuximab-resistance in head and neck squamous cell carcinoma [69], second-generation epidermal growth factor receptor (EGFR)-TKI resistance in lung cancer [70], leukemic stem cell chemoresistance in acute myeloid leukemia [71], chemoresistance of HCC via autophagy [42], and chemotherapy resistance of mouse WAP-SVT/t breast cancer cells [72].