ARPIN and breast cancer: The Arp2/3 complex is overexpressed in many cancers.1 In the case of breast cancer, the overexpression of the Arp2/3 complex, of the WAVE complex, or down-regulation of ARPIN expression was associated with poor survival.36–38 Given the paralogous specificity of Arp2/3 complexes transducing cell cycle progression, we systematically analysed the deregulation at play in the expression of all Arp2/3 complex subunits in a large cohort of breast cancer patients.