PLK1 and cancer: Furthermore, we confirmed that the mRNA levels of MASTL and PLK1 were overexpressed in breast cancer tissues compared to in their normal counterparts, as determined by the analysis of 46 pairs of breast cancer tissues and their matched non-tumor adjacent tissues, (Fig. 1f, g) and in various subtypes of breast cancer cell lines compared with normal breast cells (Fig. 1h), respectively, which indicated that MASTL expression may be associated with the mitotic activity of cancer cells.