Extramammary Paget's disease (EMPD) is a rare
skin cancer of the genital region in which
cancer cells with enlarged nuclei and pale cytoplasm are scattered singly in the affected epidermis. These
cancer cells, called Paget cells, contain
mucin, which is never found in normal epidermis. The
oligosaccharide side chains of Paget cell
mucin end with
sialic acid.
Sialic acid is easily detected by zirconyl haematoxylin or
alcian blue. The other
sugars in the
oligosaccharide chains can be detected by the
periodic acid-Shiff reaction. Rarely, the diagnosis of EMPD is complicated by the absence of
mucin from the Paget cells. We have examined such an atypical case. The
oligosaccharide side chains, including the
sialic acids, are absent. In both this case and a typical case, the Paget cells contain
epithelial membrane antigen mucin (MUC1) core
protein and usually contain gastric surface-type
mucin (MUC5AC) core
protein, which can be stained by
antibodies. Since neither core
protein is found in normal epidermis,
epithelial membrane antigen core
protein may be the most reliable diagnostic marker for
extramammary Paget's disease. In both the atypical case and the typical case of Paget's disease, some cells that look like keratinocytes contain
mucin core
proteins. These may be incipient Paget cells. We suggest that using th
epithelial membrane antigen core
protein as a marker for the true extent of
extramammary Paget's disease could facilitate complete excision and reduce the rate of recurrence.