As there is no reason to propose that the known receptor cargoes of Rab17-regulated transport – such as dlgA and TfnR – would be drivers of the DCIS to IDC transition or cancer invasiveness, we developed an unbiased mass spectrometry (MS)-based proteomic approach to investigate the Rab17 interactome and the protein cargoes whose trafficking it influences. The gene discussed is RAB17; the disease is ductal breast carcinoma in situ.