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MALIGNANT SKIN APPENDAGE NEOPLASMS

Sebaceous carcinoma and epithelioma

These are both rare tumors, which are considered together as they are both associated with internal carcinomas (see under Torre-Muir syndrome). The unclear derivation and pathological overlaps have led to the suggestion that the term sebaceous epithelioma should be dropped. Both have clinical morphology that may mimic basal cell or squamous cell carcinoma, and both occur mainly on the head and neck in older patients. Sebaceous carcinoma (Fig.23.50) has a particular tendency to occur on the upper eyelid, which is a rare site for the more common epidermal neoplasms. Sebaceous epithelioma (Fig.23.51) may be locally recurrent but has essentially benign behavior, whereas sebaceous carcinoma has a significant risk of metastasis or local recurrence after surgical excision. The most likely differential diagnosis for either of these is squamous cell carcinoma; most are diagnosed only when excised and submitted for histologic examination.

Torre-Muir syndrome

This is an autosomal dominant disorder consisting of various sebaceous tumors and visceral malignancy, usually colonic carcinoma but also cancers of ovary, uterus, and other gastrointestinal sites. Colonic polyps are frequently present. A single sebaceous tumor is adequate for the diagnosis if associated with internal tumors, but lesions are often multiple. Sebaceous adenoma (Fig.23.52) is the most common and specific type of skin neoplasm in this syndrome. Keratoacanthomas, usually multiple, are also a feature in some individuals. Both the sebaceous tumors and the internal tumors in Torre-Muir syndrome tend to be less aggressive than the same tumors occurring on a sporadic basis.

Other malignant skin appendage tumors

Most of the skin appendage tumors exist in benign and malignant forms, but in general the malignant versions are very uncommon. The nomenclature is simple, in that most such tumors are just prefaced by ‘malignant’ or sufixed by ‘carcinoma’, for example malignant eccrine spiradenoma and malignant eccrine porocarcinoma. The eccrine malignancies are relatively non-specific clinically, usually resembling squamous cell carcinomas, and may be dificult to distinguish pathologically from metastatic adenocarcinomas. Apocrine carcinomas are even rarer.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.