Extramammary Paget's disease: evaluation of the histopathological patterns of Paget cell proliferation in the epidermis.

Extramammary Paget's disease (EMPD) is a rare malignant skin neoplasm. The prototypical pattern of tumor cell proliferation in the epidermis includes single cells and/or nest arrangements, mainly in the lower epidermis. Although other patterns have been recognized, they have not previously been investigated in detail. We aimed to examine the patterns of tumor cell proliferation in the epidermis. Surgical specimens were obtained from 38 patients with primary EMPD. We defined six patterns, in addition to the prototypical one: (i) glandular; (ii) acantholysis-like; (iii) upper nest; (iv) tall nest; (v) budding; and (vi) sheet-like. There were 26 males and 12 females (mean age, 75.0 years). Lesions were located on the scrotum (26 cases) and vulva (12). There were 22 in situ EMPD and 16 invasive EMPD. The frequencies of the different proliferation patterns were: glandular, 36.8%; acantholysis-like, 73.7%; upper nest, 68.4%; tall nest, 28.9%; budding, 47.4%; and sheet-like, 23.7%. Upper nest pattern and the presence of more than three patterns were significantly more frequent in invasive EMPD than in situ EMPD (P < 0.05). We identified the histopathological patterns of Paget cell proliferation in the epidermis in EMPD, and suggest that the characteristic patterns and the diversity of patterns could be associated with progression and dermal invasion in EMPD.