PLK1 and neoplasm: In an attempt to identify biomarkers that predict response to ER maleate, we showed ER maleate-mediated downregulation of Syk and PLK1 expression in vitro correlated with its tumor regression effects and decrease in Syk and PLK1 expression in treated mice xenografts in vivo. Our clinical studies using OSCC patients' tumor sections showed Syk and PLK1 overexpression in tumors that had prognostic relevance in follow up studies, suggesting their biomarker potential.