Co-mutations of <i>CTNNB1</i> and <i>PTEN</i> drive aggressive tumor progression in endometrial cancer

Endometrioid endometrial cancer (EEC) is the most prevalent gynecological malignancy. While early-stage EEC typically carries a favorable prognosis, late-stage EEC shows significantly poorer outcomes, with a five-year survival rate of only 17-19%. Co-occurring PTEN and CTNNB1 variants are frequent in EEC and linked to poor prognosis. To investigate their functional impact, we generated uterine-specific Pten knockout mice and dominantly stabilized Ctnnb1 mutant mice (Pgrcre/+Ptenf/fCtnnb1f(ex3)/+; Ptend/dCtnnb1f(ex3)/+). These double-mutant mice exhibited significantly reduced survival compared to single Pten knockout (Pgrcre/+Ptenf/f; Ptend/d) mice. Histopathology revealed aggressive, metastatic endometrioid cancer in Ptend/dCtnnb1f(ex3)/+ mice; these mice developed myometrial invasion by four weeks of age - unlike Ptend/d mice. Transcriptomic analysis identified activation of multiple oncogenic pathways, including WNT/CTNNB1, PI3K/AKT, basal cell carcinoma, sonic hedgehog signaling and epithelial-mesenchymal transition (EMT). Immunohistochemistry confirmed hallmark features of EMT in the uterus of double-mutant mice, including strong downregulation of E-cadherin (CDH1) and upregulation of the EMT regulator SNAIL (Snai1). These findings demonstrate that synergistic mutations of PTEN and CTNNB1 promote early invasion, EMT activation, and metastatic progression, offering mechanistic insight into the aggressive behavior and poor clinical outcomes associated with this subtype of EEC.