SEBACEOUS EPITHELIOMA (SEBACEOMA)
This sebaceous tumor has been defined as one that lacks the cytologic evidence of malignancy that is seen in sebaceous carcinomas, but  is composed of less than 50% of cells having sebaceous differentiation. The latter criterion plus the presence of multiple tumor lobules separated by dermis help distinguish this tumor from sebaceous adenomas.  There can be overlap in the features of sebaceous adenomas and sebaceous epitheliomas. 'Sebaceoma' is another term that may be applied to this tumor. Sebaceous epitheliomas as well as sebaceous adenomas may be part of Torre's syndrome (classically sebaceous adenoma/s plus internal malignancy with a history of inheritance).

Regarding terminology:  Traditional pathologists designate some infiltrating epithelial tumors of skin that rarely metastasize as 'carcinoma' as in 'basal cell carcinoma'. Traditional dermatologists have used the term 'epithelioma' for some of the same tumors as in 'basal cell epithelioma'. Since the cytologically malignant sebaceous carcinoma can metastasize, the traditional pathologist cannot use the term 'carcinoma' for this tumor because it does not metastasize. Therefore, by necessity, another term is used (epithelioma). That being said, the term epithelioma implies locally aggressive behavior to some people, so it might be better to abandon the  term sebaceous epithelioma altogether and opt for sebaceoma.

Occasional basal cell carcinomas and adnexal tumors  have a  component of sebaceous cells, and such tumors are classified as per the background tumor. Sebaceous differentiation is rarely seen in salivary gland tumors.
 
Scan power view . Multiple tumor lobules of varying size and shape are separated by varying amounts of dermal collagen.
High power of the upper right part of the picture above. Very few cells have sebaceous differentiation. The other cells are 'primordial', but there is no palisading of nuclei or significant spindle cell differentiation.
High power view of another tumor lobule.
High power view of another tumor lobule. Approximately 50% of the cells have sebaceous features. There is more variation in the size of the vacuoles than one sees in clear cell tumors of sweat unit origin.
Low power view from a deep lobule of tumor.
High power of above. Prominent  duct differentiation is present, and, in this context, is interpreted as sebaceous duct differentiation. 

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