KRT14 and neoplasm: We have also shown that after tamoxifen treatment, the residual WT-PyMT tumor cells become highly enriched in CK14 expression with modestly diminished CK8 expression (Supplementary Fig. 3e, mock vs. tamoxifen: 1 vs. 7.6- fold (CK14), 1 vs. 0.6- fold (CK8)), suggesting that tamoxifen likely targets CK14-negative luminal cells, and that CK14-positive cells, including the CK14+CK8+ bi-lineage progenitor cell population and the CK14+CK8−basal/myoepithelial cell population, are likely resistant to tamoxifen.