To avoid affecting multiple pathways with small-molecule GRP78 inhibitors, we used EGF-SubA,13 a targeted fusion toxin containing catalytic subunit A of subtilase cytotoxin, whose only target is GRP78.12 To examine cytotoxic effects of PDT+EGF-SubA, five different EGFR-positive human cancer cell lines were used: two prostate cancer cell lines (DU-145 and PC-3), a lung cancer cell line (SW-900), and two colon cancer cell lines (LoVo, HCT-116). This evidence concerns the gene PCSK5 and colonic neoplasm.