ERBB2 and breast cancer: Important though is the fact that in the HER2 positive tumors we never find hypermethylation of more than 50% of ITGA4 alleles (Figs. 5, 7) and BC samples with completely nonmethylated ITGA4 also exist, which suggests that simultaneous expression of HER2 and integrin α4 is not lethal, but rather renders some evolutionary disadvantage for the tumor cells that acquire such expression pattern.