APC2 and breast cancer: Although it is known that both Apc and Apc2 are able to regulate Wnt signaling,12, 13, 14 and that this pathway is frequently mis-regulated in many human cancers including breast cancer,1, 5, 6, 7, 8, 9, 10, 11 non-synonymous mutations in these genes within mammary tumors are rare.5, 6 The interplay between Apc and Apc2 in this setting has never before been explored.