Phosphoinositides play pivotal roles in the regulation of cancer cell phenotypes. Among them, phosphatidylinositol 3,4-bisphosphate (PI(3,4)P ) localizes to the invadopodia, and positively regulates tumor cell invasion. In this study, we examined the effect of PI(3,4)P on focal adhesion dynamics in MDA-MB-231 basal breast cancer cells. Knockdown of SHIP2, a phosphatidylinositol 3,4,5-trisphosphatase (PIP ) 5-phosphatase that generates PI(3,4)P , in MDA-MB-231 breast cancer cells, induced the development of focal adhesions and cell spreading, leading to the suppression of invasion. In contrast, knockdown of PTEN, a 3-phosphatase that de-phosphorylates PIP and PI(3,4)P , induced cell shrinkage and increased cell invasion. Interestingly, additional knockdown of SHIP2 rescued these phenotypes. Overexpression of the TAPP1 PH domain, which binds to PI(3,4)P , and knockdown of Lpd, a downstream effector of PI(3,4)P , resulted in similar phenotypes to those induced by SHIP2 knockdown. Taken together, our results suggest that inhibition of PI(3,4)P generation and/or downstream signaling could be useful for inhibiting breast cancer metastasis.