PI3 Kinase (PI3K) signalling has been associated with the development and progression of many cancer types including colorectal cancer (CRC). This signalling cascade is typically initiated via growth factors such as EGF, resulting in activation of receptor tyrosine kinases (RTKs). The most characterised canonical pathway explored in the development of disease occurs at the cell membrane, where PI(4,5)P2 is converted to PI(3,4,5)P3. PI(3,4,5)P3 propagates the signal by recruiting proteins containing specific phosphoinositide binding domains (e.g PH domains). Among these is the serine-threonine kinase AKT, which transduces its signal to a range of downstream substrates affecting cell proliferation, growth, survival, apoptosis, protein synthesis and glucose metabolism. While the conventional view is that PI3K signalling propagates from the plasma membrane, we have discovered evidence of nuclear PI3K signalling in CRC. Using the GST-tagged reporter protein GRP1PH and an anti-PI3K catalytic subunit p110α antibody, we have shown that ~30% of primary cancers and human CRC cell lines exhibit nuclear localisation of PI(3,4,5)P3. This nuclear pool responds to EGFR activation, perhaps through receptor shuttling, and is able to be inhibited by EGFR inhibitors. Using Reverse Phase Protein Arrays (RPPA) technology, we have identified proteins that differ in their phosphorylation state in the nuclear PI3K cell lines, suggesting potential members of the nuclear PI3K signalling cascade. The utilisation of RNA-Seq and proteomic studies have led to the identification of the nuclear PI(3,4,5)P3 interactome and the identification of a role for nuclear PI3K signalling in processes such as RNA splicing and gene expression. Finally, we have observed an increase in sensitivity towards MEK inhibition in nuclear PI3K cells, suggesting the potential for MEK inhibition as a targeted therapy for patients exhibiting tumour nuclear PI3K.