Our PI(3,4)P2 biosensor imaging experiments performed in normal HEK-293 cells, together with our previous immunostaining-based findings in MDA-231 breast cancer cells (23) not only strengthen Pfn1-dependent regulation of PI(3,4)P2 in a general context, but also demonstrate that loss of Pfn1 expression increases biosynthesis of PI(3,4)P2 rather than slowing its degradation. The gene discussed is PFN1; the disease is breast cancer.