RO3280 and GSK461364 areselective ATP-competitive inhibitors ofPolo-like kinase (PLK1).1−3 PLK1 belongs to a family of serine/threonineprotein kinases, which plays a key role as a regulator of cell-cycleregulation.4 This protein is also involvedin cancer progression and is overexpressed in malignant cells andsolid tumors (lung, breast, ovary, stomach, colon).5 For this reason, PLK1 has emerged as an attractive targetfor cancer therapy.3 PLK1 inhibition resultsin the death of cancer cells by interfering with the cell cycle. This evidence concerns the gene PLK1 and cancer.