CD44 distribution in sweat gland tumors suggests it has different functional roles in the various cell types.

CD44 is a polymorphic group of membrane glycoproteins with multiple functions that include cell adhesion. Since on normal sweat glands CD44 is expressed only in eccrine coil secretory cells, it has been considered as a possible marker of this type of differentiation. We have immunohistochemically investigated the distribution of CD44 in paraffin-embedded samples of 41 benign and malignant sweat gland tumors by using a monoclonal antibody directed against the standard isoform of CD44. CD44 was strongly expressed in epithelial cells at the peripheral row of syringomas and in cuticular areas of eccrine poromas. Apocrine tumors such as apocrine hidrocystoma, syringocystadenoma papilliferum, or hidradenoma papilliferum showed intense CD44 positivity in the portion of cells in contact with the neighboring stroma and focally on the luminal side of cells with apocrine secretion. Cylindromas and spiradenomas presented focal CD44 positivity, virtually limited to clear cells. Malignant neoplasms exhibited irregular CD44 staining, which was more intense in the less differentiated zones and tumors. Our results indicate that CD44 is not a useful marker for a specific form of sweat gland differentiation. Nevertheless, its characteristic patterns of distribution might reflect the variety of functional roles assumed by the different CD44 isoforms in each epithelial cell.