Uroplakin-III to distinguish primary vulvar Paget disease from Paget disease secondary to urothelial carcinoma

Paget disease of the vulva can be mimicked by several disease entities histopathologically, but most of these entities can be clinically distinguished from vulvar Paget disease. However, vulvar Paget disease is in itself a heterogeneous group of epithelial neoplasms that can be similar both clinically and histopathologically. The subtypes of vulvar Paget disease include primary Paget disease arising from a pluripotent stem cell within the epithelium of the vulva, and secondary Paget disease of the vulva. Secondary vulvar Paget disease results from spread of an internal malignancy, most commonly from an anorectal adenocarcinoma or urothelial carcinoma of the bladder or urethra, to the vulvar epithelium. We have recently proposed that these lesions be classified as primary (of cutaneous origin) or secondary (of extracutaneous origin). These subtypes can present similarly as eczematoid skin lesions and may appear similar on routine hematoxylin and eosin-stained slides. Immunohistochemical studies can help differentiate between them. Our current study includes 17 patients with a pathologic diagnosis of vulvar Paget disease. We performed a panel of immunohistochemical stains, including cytokeratin (CK) 7 and 20, carcinoembryonic antigen (CEA), gross cystic disease fluid protein-15 (GCDFP-15), and uroplakin-III (UP-III). Of these 17 patients, 14 (80%) had primary intraepithelial cutaneous Paget disease, 13 without invasion and 1 with associated invasion. Three patients had urothelial carcinoma with spread to the vulva, manifesting as secondary vulvar Paget disease. Immunohistochemically, primary vulvar Paget disease is immunoreactive for CK 7 and GCDFP-15, but uncommonly for CK 20. Vulvar Paget disease secondary to anorectal carcinoma demonstrates CK 20 immunoreactivity but is usually nonreactive for CK 7 and consistently nonimmunoreactive for GCDFP-15. Vulvar Paget disease secondary to urothelial carcinoma is immunoreactive for CK 7 and CK 20 but nonimmunoreactive for GCDFP-15. In addition, we propose the use of a new, commercially available antibody, UP-III, which is specific for urothelium and, in our experience, is immunoreactive in secondary vulvar Paget disease of urothelial origin. The distinction between these 3 types of Paget and Paget-like lesions is essential in that the specific diagnosis has a significant influence on current treatment. The difference in surgical approach to the subtypes of vulvar Paget disease justifies classifying them into distinct lesions, which may be aided by the use of immunohistochemistry, including UP-III.