Mutations at serine 33 (S33) and serine 37 (S37) in β-catenin are key oncogenic events, disrupting normal regulation by preventing phosphorylation-dependent degradation and resulting in β-catenin stabilization, nuclear accumulation, and tumorigenesis. The β-catenin S33/S37 mutation lentivirus (C-terminal FLAG tag, TET-inducible, Puro) expresses the β-catenin S33A/S37A mutant with a C-terminal FLAG tag, under the control of the TRE3G promoter with puromycin as a selection marker. With the PGK promoter-driven Tet-On 3G, β-catenin expression can be induced by doxycycline.