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  • Cutaneous appendage tumors are classified into eccrine, apocrine, follicular, and sebaceous entities, and can be benign or malignant.

  • Clinically, appendage tumors are dermally based, usually with minimal epidermal change, and histopathologic evaluation is necessary to make a diagnosis.

  • Certain appendage tumors can serve as markers for genetic diseases and syndromes.

Cutaneous appendage (adnexal) tumors encompass both benign and malignant neoplasms and have been traditionally classified by their line of differentiation toward normal adnexal structures of the skin: eccrine, apocrine, follicular, and sebaceous (Table 109-1).1-3 Many specific types of appendage tumors have been described, and rather than providing an exhaustive list, this chapter focuses on the more common and/or clinically significant tumors. In general, with some exceptions, appendage tumors are relatively rare. Benign appendage tumors have no potential to metastasize, whereas malignant appendage tumors do. There is also a subset of tumors that may be locally aggressive but are not associated with metastasis. Appendage tumors may occur sporadically or may serve as markers of rare genetic syndromes, including Muir-Torre syndrome, Cowden syndrome, Birt-Hogg-Dubé syndrome, and Brooke-Spiegler syndrome. We describe the clinical and histopathologic features with an emphasis on differential diagnosis and tumor biology.

Table 109-1Classification of Cutaneous Appendage Tumors

The clinical presentation of appendage tumors is most commonly that of solitary or multiple dermal papule(s) or nodule(s), with minimal overlying epidermal changes. The tumors may appear skin-colored, pink, or with a bluish hue. The presence of a hair follicle orifice or other central punctum may be seen. Some appendage tumors have specific site or age predilections, which may help in the differential diagnosis. Although the patient’s age, gender, site of presentation, and clinical morphology may lead one to suspect an appendage tumor, biopsy with subsequent histopathology is usually required for diagnosis. Careful review of routinely processed hematoxylin-and-eosin–stained slides is often the most important part in making the diagnosis of an appendage tumor. An adequate sample is necessary given the heterogeneity of many tumors and the histologic overlap between appendage neoplasms. Furthermore, analysis of the architecture is often necessary in diagnosing appendage tumors, especially when distinguishing between benign and malignant neoplasms. Immunohistochemistry ...

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