Primary extramammary Paget's disease: a clinicopathological study of 28 cases.

To analyze the clinical and histopathological manifestations, immunohistochemistry, treatment, and prognostic factors of primary, extramammary Paget's disease (EMPD), we systematically reviewed the clinical presentations, histopathology and follow-up courses of 28 patients with primary EMPD. Clinically, their symptoms and morphology mimicked various types of dermatoses, such as seborrheic dermatitis, eczema, candidiasis, tinea cruris and erythrasma, so the initial diagnosis of EMPD was often delayed or missed. Histopathology showed invasive EMPD, and the tumor cells were mostly solid nests or had a glandular structure. The cellular atypia was obvious and signet ring Paget's cells could usually be observed. The acantholysis phenomenon in the epidermis could be seen. The condition was associated with stromal invasion, lymphatic metastasis, and even vascular invasion. Adnexal involvement in primary EMPD was a very common feature. The immunohistochemical markers CK7, GCDFP-15, CEA and HER-2 positive can identify other tumors similar to Paget's disease. We concluded that invasive EMPD is a rare malignant skin neoplasm with morphological diversity. Poorly differentiated cell morphology, extensive adnexal involvement, and an invasive pattern of solid sheets are significantly associated with lymph node metastasis and a worse prognosis. Pathologists should be alert to invasive lesions and make the correct diagnosis.