Sustained activation of ER-K-ras^G12D induced by tamoxifen treatment is important for cell proliferation, anchorage-independent cell growth, cell invasiveness and tumor maintenance.

<p>A) Cell number counting of indicated MEFs after withdrawal of tamoxifen after 6 passages in the presence of tamoxifen. The PEK-C MEFs always without tamoxifen treatment and the PEK-C MEFs always kept in tamoxifen were used as control. B) Tamoxifen were withdrawn from the PEK-C MEFs at day 5, 10 and 28 after continuous tamoxifen treatment in soft agar. C) Tamoxifen withdrawal from the PEK-C MEFs after indicated days of tamoxifen treatment in cell invasiveness assay in matrigel. D) Tamoxifen withdrawal for indicated time in the <i>P53L/L</i>, <i>LSL-ER-K-ras^G12D</i> mice previously treated for 12 weeks of tamoxifen. The typical lung pathology and cleaved caspase-3 immunostaining were shown.