Based on various studies showing that the gastrin-releasing peptide (GRP, an autocrine growth factor) receptor is up-regulated on the surface of different malignant cell types including cell lines from small cell lung, breast, prostate, and colon cancers (Carney et al., 1987; Schutte and Seeber, 1993), an immunotoxin with GRP has been produced (DT389-GRP). This evidence concerns the gene GRP and malignant colon neoplasm.