Wnt was first associated with tumorigenesis with the discovery that overexpression of int1 (Wnt1), then found to be an ortholog of wg, generated mammary hyperplasia and breast tumors in mice (Nusse et al., 1984; Rijsewijk et al., 1987; Tsukamoto et al., 1988). Here, WNT1 is linked to breast neoplasm.