SPP1 and penile cancer: Many studies have described the overexpression of SPP1 in multiple cancers such as breast carcinoma [17], hepatocellular carcinoma [18], penile cancer [19], ovarian carcinoma [20], and lung adenocarcinoma [21], as well as the key roles of SPP1 in invasion, metastasis, chemoresistance, and immune suppression [22,23].