SEBACEOUS ADENOMA
The prototypic sebaceous adenoma is composed of an expansile mass of sebaceous units communicating with the epidermal surface along multiple points. This is in contrast with sebaceous hyperplasia where the sebaceous units insert into a common lumen. Most sebaceomas are located predominately within the dermis and have few, if any, epidermal connections.

Most of the cells within the sebaceous units in sebaceous adenomas as well as in sebaceous hyperplasia are mature (well-differentiated). Holocrine secretion near the surface may be easily discerned in most sebaceous adenomas. In contrast, a smaller percentage of the tumor cells are well-differentiated in sebaceomas. Mitoses are uncommon in sebaceous adenomas.

Multiple sebaceous adenomas and multiple sebaceomas are part of the Muir-Torre syndrome.


Solitary tumor from the back (posterior thorax) of a 60 year old male:
 
Very low power (direct scan of glass slide) view. The tumor communicates with the surface in multiple points, and holocrine secretion is prominent along the surface.
Low power view. Note the holocrine secretion along the surface.
High power view. Most of the tumor cells have well-differentiated sebaceous cytology.

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