RNAi of candidate Wnts identifies Wnt1, Wnt2, Wnt3, and Wnt7b as the specific isoforms mediating autocrine Wnt signaling in tumor cell lines M14 (melanoma), NCI-H23 (NSCLC), PA-1 (teratocarcinoma), and Hs578T (breast), respectively. Here, WNT3 is linked to melanoma.