The results of Tas et al., Demiray et al. and this study are however inconsistent with the findings of a research by Krawczyk et al., where the incidence of M30 in breast tumor tissue was investigated by immunohistochemistry and the results showed higher incidence of this cytokeratin in hormone-positive and HER2-positive subtypes and cancers with lower grade tumors (23). This evidence concerns the gene ERBB2 and breast neoplasm.