Phosphoinositol–3kinase (PI–3K) is another important pathway that mediates estrogen action. There are three class of PI–3K; class I (IA and IB), class II, and class III. It is now accepted that class I PI–3K activation is one of the most important signaling transduction pathway to modulate intracellular events including cell growth, survival, proliferation, and movement (Hawkins et al. 2006).