It has been claimed that palmar and plantar keratoses are more common in individuals with bladder and lung cancer, occurring in 70–90 % of cases and in only 36 % of controls, but it is difficult to assess the significance of this finding since it is based on only a few studies (Cuzick et al. 1984). Keratin gene or connexin abnormalities may underlie this group of conditions (Bale and DiGiovanna 1997; Kelsell et al. 2000; Kimyai-Asadi et al. 2002; Radi et al. 2005).
There are many subtypes, including palmoplantar keratoderma, the Clarke–Howel–Evans syndrome (see Esophageal Cancer) (Malde, Meleda, Smith 2003). Mutations of the KRT1 and KRT9 genes may cause the epidermolytic form of PPK. Both epidermolytic and nonepidermolytic forms of palmoplantar keratoderma have been observed with various mutations in the KRT1 gene (Chiu et al. 2007).