EGFR and neoplasm: For EGFR conditional TCEs (131–133), dual-masking was deployed to mask the TAA as well as the CD3 binder, such as in the Probody CX-904 molecule (132), due to persistent on-target toxicity concerns with single-mask approaches, whereas an elegant design called COBRA physically disassembled the CD3 binder in its inactive form to prevent any off-tumor binding (Figure 3-3) (134).