Malignant sweat gland tumors: an update.

Sweat gland carcinomas represent an important and somewhat contentious group of tumors in diagnostic skin pathology. Although their overall incidence is rare, they show a wide range of histologic features, and reliable classification is often challenging. Awareness and recognition of these tumors is, however, important as they may be associated with significant morbidity and even disease-related mortality, especially if left untreated. According to their behavior, sweat gland carcinomas are traditionally separated into tumors with low-grade and high-grade malignant behavior. This article is aimed at increasing awareness and providing an overview of malignant sweat gland tumors with emphasis on recently reported and novel findings and diagnostically challenging and potentially underrecognized entities. It further aims to illustrate the wide morphologic range of these tumors and provides a discussion of the relevant immunohistochemistry, disease-specific behavior, and differential diagnosis.