A similar immunotoxin, IL‐4(38–37)‐PE38KDEL, comprised of a circularly permutated human IL‐4 fused with Pseudomonas aeruginosa exotoxin A, was found to be cytotoxic against the human breast cancer cell line, MDA‐MB231, both in vitro and in murine xenograft models [41]. This evidence concerns the gene IL4 and breast carcinoma.