clonal seborrheic keratosis, large cell variant

VARIANT OF CLONAL TYPE OF SEBORRHEIC KERATOSIS

From an adult.

Clonal (nesting) seborrheic keratoses are characterized by the presence of nests of cells that differ morphologically from their neighbors within the background of a seborrheic keratosis. In the usual case, the nests are composed of cells smaller than the adjacent keratinocytes, but there are cases where the cells are larger or where there are other morphologic differences as in this case. Transitional forms between cells within the nests and the adjacent keratinocytes are often seen. These cell nests are not to be confused with the squamous eddies that are found in irritated seborrheic keratoses. Clonal seborrheic keratoses are distinguished from intraepidermal porocarcinomas and from Bowen's disease by the lack of atypia, and, in the case of intraepidermal porocarcinoma, by the lack of carcinoembryonic antigen positivity. Cases that were clonal seborrheic keratoses were included by some pathologists in the diagnosis of intraepidermal epithelioma of Borst-Jadassohn thereby adding to the confusion associated with that term. Clonal seborrheic keratoses may be misdiagnosed as hidroacanthoma simplex, a very rare lesion.

The cells within the nests were unusual in this case, so I had sections examined for carcinoembryonic antigen, and this study was negative.

Composite scan power view.

Low power view of the area in the yellow rectangle. There are nests of cells that contrast morphologically with their neighbors. Some of the cells are spindle shaped.

High power view of above. The cells within this nest have cytoplasm that is clearer than that of the adjacent keratinocytes, but sebaceous differentiation is not seen. Transitional forms are seen at the junction of the abnormal nest and the adjacent keratinocytes.

Low power view of red rectangle.

High power of above. This picture is a lesson in honesty. There are transitional forms in the nest in the right side of the picture but not in the nest in the left side of the picture. We tend to photograph findings that fit our bias.

Low power view from green rectangle. Some of the cells in these nests are smaller than the neighbors, and, therefore, are more like those found in a classical clonal seborrheic keratosis. Transitional forms are in the nest to the right but less apparent in the nest to the left.

Low power view from black rectangle. This field has the classical features of a seborrheic keratosis.

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	Low power view of the area in the yellow rectangle. There are nests of cells that contrast morphologically with their neighbors. Some of the cells are spindle shaped.
	High power view of above. The cells within this nest have cytoplasm that is clearer than that of the adjacent keratinocytes, but sebaceous differentiation is not seen. Transitional forms are seen at the junction of the abnormal nest and the adjacent keratinocytes.
	Low power view of red rectangle.
	High power of above. This picture is a lesson in honesty. There are transitional forms in the nest in the right side of the picture but not in the nest in the left side of the picture. We tend to photograph findings that fit our bias.
	Low power view from green rectangle. Some of the cells in these nests are smaller than the neighbors, and, therefore, are more like those found in a classical clonal seborrheic keratosis. Transitional forms are in the nest to the right but less apparent in the nest to the left.
	Low power view from black rectangle. This field has the classical features of a seborrheic keratosis.