EGFR and breast cancer: In another study by Lim et al., modified Pseudomonas exotoxin A (PE38), a natural ligand of epidermal growth factor receptor (EGFR) when expressed in Salmonella typhimurium, led to the inhibition of the solid tumor growth in mice implanted with colon cancer cells and 4T1 breast cancer cells having considerable EGFR expression [21].