General Principles for the Histopathologic Diagnosis of Neoplasms with Eccrine and Apocrine Differentiation. Classification and Histopathologic Criteria for Eccrine and Apocrine Differentiation

Abstract

Eccrine and apocrine ducts are histologically, immunohistochemically, and ultrastructurally indistinguishable.

Secretory apocrine differentiation consists of the presence of the so-called decapitation secretion in the luminal border of tubular structures.

“Fringe” or “threads” in the luminal border of cells seem to represent a minimal expression of decapitation secretion.

Vacuoles forming a ring at the periphery of the glandular lumen and surrounding an eosinophilic and homogeneous material also result from apocrine secretion.

Mucinous cells are frequency seen in the luminal border of the ductal formations of apocrine hidradenoma. Polygonal, plasmacytoid, or hyaline cells are especially frequent in apocrine mixed tumor and apocrine hidradenoma.

Elongated ducts lined by a double layer of epithelial cells are seen mostly in apocrine mixed tumor. Secretion by decapitation is sometimes observed in the cells that line the luminal border of these elongated ducts.

Papillary formations are also frequently seen in neoplasms with apocrine differentiation.

Connection of tubular structures of the neoplasm with pre-existing follicular infundibula, reproducing the connection that takes place in normal skin among the excretory duct of the apocrine glands, and the follicular infundibulum is seen in some neoplasm with apocrine differentiation.

Evidence of follicular and/or sebaceous differentiation in a neoplasm with ductal differentiation is indicative of apocrine differentiation based on the common embryological origin of the three elements of the folliculo-sebaceous–apocrine unit.