In both breast and pancreatic cancer cells, RAC1 is a downstream effector of ERBB receptors and mediates migratory responses by ERBB1/EGF receptor (EGFR) ligands such as EGF or TGF-α and in breast cancer cells also by ERBB3 ligands such as heregulins. This evidence concerns the gene RAC1 and familial pancreatic carcinoma.