ANPEP and pachyonychia congenita: The APN serum concentration in PC patients was significantly higher than in all others.43 An increased expression of APN was also immunohistochemically detected in a gallbladder tissue of patients with squamous cell/adenosquamous carcinoma (SC/ASC) together with similarly increased expression of aconitase (E.C. 4.2.1.3), which is also similarly overexpressed.