CEACAM5 and neoplasm: Based on our observations, α-CEA-680-PTX localizing to a BxPC-3 tumor in vivo may exhibit three potential outcomes; a) α-CEA-680-PTX localizes to the tumor site, but paclitaxel has already been hydrolyzed from the antibody en route due to linker lability (Fig 2); b) α-CEA-680-PTX localizes, is internalized with CEA, digested via lysosomal degradation, and the drug is released intracellularly; or c) α-CEA-680-PTX localizes, paclitaxel is hydrolyzed from the antibody before internalization occurs, released to the local extracellular environment, and passively diffuses into target cells.