Large cells may constitute all or part of the atypical cell population in the epidermis in extramammary Paget's disease.

This case also illustrates the 'sparing' of the basal layer that may be more apparent than real. Contact with the basement membrane may actually be present, but a section through the edge of an expansile cluster of the atypical cells may give the false impression that there is no contact with the basal layer. This 'sparing' of the basal layer can also be seen in some examples of Bowen' disease and, less commonly, in actinic keratoses. This type of 'sparing' is very rare in the intraepidermal component of melanomas.

Note: Diastase digestion did not precede the PAS stains on this case. Therefore, glycogen is seen in some of the normal keratinocytes.
 
 

	Medium power view. A few of the atypical cells are in a pagetoid distribution, but many are found singly or in clusters in the lower epidermis.
	High power view. The vacuolated cytoplasm and the presence of basophilic mucin with the cytoplasm of some of the cells are diagnostic in this setting.
	High power view, PAS stained. The BL arrow points to the basal layer. The BM arrow points to the basement membrane. This gives the appearance of sparing of the basal layer by the clusters of atypical cells. If, however, the cluster of atypical cells has a convex border, a section through the edge of such a cluster would give this appearance whether it touched the basement membrane or not.
	Another high power view that is PAS stained. The BMarrow points to the basement membrane. The atypical cells touch the basement membrane.

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