The results in this work indicate that ABCG2 gene is not expressed or is slightly expressed in normal breast tissue resistant to carcinogenesis induced by Maitake, but is expressed in breast tumors treated or untreated with Maitake, suggesting probably that ABCG2 gene expression could have a complementary role involved the oncogenesis de‐differentiation, meaning that when is over‐expressed, increases the tumorigenic potential of transformed cells, and the resistance to multidrugs, as occuring in the breast tumors treated or untreated with Maitake. Here, ABCG2 is linked to breast neoplasm.