The key findings of this study are that MMTV-ΔN89β-catenin and MMTV-Wnt1 induce distinct tumors, activate canonical signaling in disparate cell-types, and MMTV-Wnt1 alone results in focal Hh pathway activity within the mammary tumor microenvironment and in and around melanocytic hyperplasia. This evidence concerns the gene WNT1 and breast cancer.