Ultrastructural Examination of a Case of Pagetoid Bowen Disease Exhibiting Immunohistochemical Features in Common With Extramammary Paget Disease.

A panel of immunohistochemical markers may be used to differentiate between pagetoid Bowen disease (PBD) and primary extramammary Paget disease (EMPD) in selected cases. Although diffuse staining with cytokeratin 7 (CK7), CAM5.2, carcinoembryonic antigen, epithelial membrane antigen (EMA), and gross cystic disease fluid protein 15 generally supports diagnosis of EMPD, cases have been reported where PBD also expressed CK7, EMA, and CAM5.2. Based on these findings, some authors suggested that the 2 entities may arise from the same multipotent stem cell, capable of further differentiation toward squamous and secretory lines. To the best of our knowledge, this issue has never been investigated by comparing PBD and EMPD at the ultrastructural level. We performed the first ultrastructural study of a case of PBD exhibiting common immunohistochemical features with EMPD. The lesion displayed some ultrastructural features often observed in Bowen disease and some that are typically found in EMPD. These findings indicate the presence of a bidirectional differentiation--secretory and squamous--within the same lesion, thus supporting the hypothesis that PBD and primary EMPD may arise from a common progenitor cell.