ESR1 and breast neoplasm: Overexpression of miR-342 upregulates the expression of ER-α mRNA and sensitizes the MCF7 cells to tamoxifen. miR-342 is down-regulated in breast tumors resistant to Tamoxifen. Reintroduction of miR-342 sensitizes refractory breast tumor cells to tamoxifen therapy. ID4 was identified as a putative target of miR-342