SPP1 and melanoma: The role of OPN in tumorigenesis, cancer progression, and survival has been demonstrated in various cancers, including glioblastoma multiforme, hepatocellular carcinoma, colorectal cancer, lung cancer, breast cancer, bladder cancer, melanoma, head and neck squamous cell carcinoma, and acute myeloid leukemia (Bramwell 2006, Le 2006, Conway et al.2009, Likui et al. 2010, Liersch et al. 2012, Güttler et al. 2013, Wang et al. 2018, Zhang et al. 2020).