In MMOC it was also observed that the hormone-independent alveolar lesions form in the absence of estrogen and progesterone; whereas the lesions developed in the presence of estrogen and progesterone were termed as hormone dependent The differential action of ERα and ERβ has only been identified recently, and few reports can be found in the literature that focus on the differential role of ERα and ERβ in breast cancer and experimental carcinogenesis [30]. This evidence concerns the gene ESR2 and breast cancer.