PLK1 and cancer: Although overexpression of PLK1 is frequently found in various human cancers, the evidence for the clinical and prognostic relevance of PLK1 is controversial in different cancer types.[10, 15] To investigate the clinical significance of PLK1 in CRC, we examined the protein level of PLK1 in CRC patient samples by using a tissue microarray (TMA) on colon or rectal tumor tissues obtained from 343 CRC patients (Table S1, Supporting Information).