Diffuse CK7, CAM5.2 and BerEP4 positivity in pagetoid squamous cell carcinoma in situ (pagetoid Bowen's disease) of the perianal region: A mimic of extramammary Paget's disease

摘要

Approximately 5% of cases of cutaneous squa-mous cell carcinoma in situ (SCCIS)/Bowen's disease exhibit a nested pattern, referred to as pagetoid SCCIS or pagetoid Bowen's disease. This growth pattern may closely simulate extramammary Paget's disease (EPD), particularly when the external genitalia or perianal region are involved, as these are the most common sites of EPD. Although in some instances it is relatively straightforward to diagnose pagetoid SCCIS on routine haematoxylin and eosin-stained sections, there are cases where it is extremely difficult to distinguish this from EPD. In morphologically problematic cases, immunohistochemical markers, including cytokeratin 7 (CK7), CAM5.2, carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA), are used frequently to differentiate between these and also pagetoid malignant melanoma in situ which may be in the differential. Diffuse staining of the atypical cells with CK7, CAM5.2, CEA and EMA antibodies supports a diagnosis of EPD. Herein, we report a case of pagetoid SCCIS of the perianal skin exhibiting diffuse staining with CK7 and CAM5.2 antibodies, this unusual and unexpected immunophe-notype resulting in misdiagnosis as EPD.