In contrast to what we have previously observed in various breast carcinoma cell lines, in which expression of the G2/M phase kinase Plk1 has been found to be transiently down-regulated following radiation exposure [7-9,19], Plk1 expression was found to be increased above control level in irradiated SW620 cells and possibly also in the HCT116 counterparts (Figure 2). This evidence concerns the gene PLK1 and breast carcinoma.