The mechanisms of granulosa cell tumor (GCT) development may involve the 
dysregulation of signaling pathways downstream of follicle-stimulating hormone, 
including the phosphoinosite-3 kinase (PI3K)/AKT pathway. To test this 
hypothesis, a genetically engineered mouse model was created to derepress the 
PI3K/AKT pathway in granulosa cells by conditional targeting of the PI3K 
antagonist gene Pten (Pten(flox/flox);Amhr2(cre/+)). The majority of 
Pten(flox/flox);Amhr2(cre/+) mice featured no ovarian anomalies, but 
occasionally ( approximately 7%) developed aggressive, anaplastic GCT with 
pulmonary metastases. The expression of the PI3K/AKT downstream effector FOXO1 
was abrogated in Pten(flox/flox);Amhr2(cre/+) GCT, indicating a mechanism by 
which GCT cells may increase proliferation and evade apoptosis. To relate these 
findings to spontaneously occurring GCT, analyses of PTEN and phospho-AKT 
expression were performed on human and equine tumors. Although PTEN loss was not 
detected, many GCT (2/5 human, 7/17 equine) featured abnormal nuclear or 
perinuclear localization of phospho-AKT, suggestive of altered PI3K/AKT 
activity. As inappropriate activation of WNT/CTNNB1 signaling causes late-onset 
GCT development and cross talk between the PI3K/AKT and WNT/CTNNB1 pathways has 
been reported, we tested whether these pathways could synergize in GCT. 
Activation of both the PI3K/AKT and WNT/CTNNB1 pathways in the granulosa cells 
of a mouse model (Pten(flox/flox);Ctnnb1(flox(ex3)/+);Amhr2(cre/+)) resulted in 
the development of GCT similar to those observed in Pten(flox/flox);Amhr2(cre/+) 
mice, but with 100% penetrance, perinatal onset, extremely rapid growth and the 
ability to spread by seeding into the abdominal cavity. These data indicate a 
synergistic effect of dysregulated PI3K/AKT and WNT/CTNNB1 signaling in the 
development and progression of GCT and provide the first animal models for 
metastatic GCT.