Background: Bowen’s disease (BD) is a skin carcinoma in situ occurring over the entire body surface. It shares similar histopathological features with Bowenoid papulosis (BP) of the genitalia, but differs in etiology and clinical course. Increased p16INK4A (p16) tumor suppressor protein expression has been demonstrated in relation to the progression of cutaneous squamous neoplasms.
Objective: To evaluate the difference in p16 expression between Bowen’s disease and Bowenoid papulosis.
Material and Method: Biopsies of 46 cases of BD in the period 1994 - 2003 and 14 cases of BP during 1987 - 2003 in the Anatomical Pathology Unit, Department of Pathology, Faculty of Medicine, Prince of Songkla University, Thailand were studied by immunohistochemical methods using the P16 kit (CINTecTM Histology Kit, clone E6H4, Code-Nr. K5334, DakoCytomation, Denmark). Nuclear/cytoplasmic immunoreactivity in more than 10% of neoplastic cells was considered positive.
Results: P16 expression was positive in 37 of 46 BD cases (80.4%) which was higher than that of BP (6 of 14 cases or 42.9%) (p value < 0.05, Chi-square test). The expression among the three groups of BD: extragenital (28 of 35), chronic arsenical-related (7 of 8) and genital lesions (2 of 3) was not significantly different (p value = 0.734, Chi-square test).
Conclusion: P16 expression was more frequent in BD than BP. This suggests a possible association between p16 expression and tumorigenesis of these lesions.

Keywords: P16INK4A, Bowen’s disease, Bowenoid papulosis