The XmAb AMG 509 features an additional anti-CD3 scFv alongside two identical anti-STEAP1 Fab regions (Fab2-scFv-Fc, Figure 1d and Table 1), showed 50-fold more potent lysis of prostate cancer cells in vitro than XmAb with a single anti-STEAP1 domain [127], and its safety and efficacy in humans is being evaluated in an ongoing phase 1 trial (NCT04221542). Here, STEAP1 is linked to Familial prostate cancer.