ERBB2 and pachyonychia congenita: An earlier report indicated that EPX was a ligand for the HER2 receptor and a source of TGF-β (Kadin et al, 1993) that induced a sustained up-regulation of MUC2 and MUC4, and showed that HER2 was associated with particularly aggressive forms of PC (Lei et al, 1995); therefore, chronic eosinophil activation and the release of EPX granules in tissues contribute to the development of malignancy by activating TGF-β and MUC2.