Updated project metadata. Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype and the lack of specific signature makes difficult the development of targeted therapeutic strategy. We previously found that PRICKLE1, an evolutionary conserved protein acting as a regulator of vertebrate development, is upregulated in TNBC. Proteomic approaches allowed us to decipher the protein complex associated to PRICKLE1 in TNBC. Within that complex, we identified a large subset of proteins involved in the regulation of Rho-GTPase family members. We build a metagene with regulators of small G-protein activity and we found that this metagene is overexpressed in TNBC and is a poor prognosis marker. We analyzed the combination of the metagene expression and PRICKLE1 expression and identified that combined expression of ECT2 and PRICKLE1 provides a worst prognosis than PRICKLE1 expression alone in TNBC. ECT2 is a GEF for Rac1 and we showed that PRICKLE1 regulate the enzymatic activity of ECT2. Finally, we also observed that Ect2 and Prickle1 are functionally connected during evolution since both act synergistically to coordinate cellular movement during vertebrate gastrulation. Our results demonstrate the pivotal role of PRICKLE1 in TNBC and build the path for development of targeted therapeutic strategies to heal TNBC patients.