ALCAM and Familial prostate cancer: To extend the finding to other tumor cells and to evaluate the impact of guide antigen internalization, we studied in vitro invasion assay in the presence of RSPO1 of prostate cancer PC3 cells that express similar levels of the non/slowly internalizing guide antigen ALCAM and the rapidly-internalizing guide antigen EphA2 (see Supplementary Table S1 for antigen density).