POU5F1 and invasive breast carcinoma: Previous analyses of OCT4 expression in human somatic tumour cell lines showed that OCT4 expression was absent in MCF‐7 and HeLa cells compared with nTera cells.25 In the Finak Breast data set, we found that the POU5F1 mRNA level was significantly decreased in invasive breast cancer compared to the breast samples with all four probes (Figure 1A).