Ectopic breast tissue and breast-like sweat gland metaplasias: an overlapping spectrum of lesions

There are many similarities in the morphology of benign and malignant lesio ns of the sweat glands and the breasts. The recently described cutaneous ma mmary-like sweat glands, also known as mixed sweat glands or apoeccrine gla nds, are also a likely source of selected proliferations that closely mimic those of the breast. We present three cases of breast-like lesions arising in the skin that demonstrate the ways in which the morphologic and patholo gic continuum of the mammary glands, cutaneous mammary-like glands, and swe at glands can produce difficulties in precise diagnosis. The examples demon strate that an anatomic location outside the milk line does not preclude th e diagnosis of ectopic mammary tissue, and that lesions closely resembling those of the breast may also arise outside the milk line from conventional sweat glands or mixed sweat glands. The concept of homologous lesions of th e breast, breast-like glands and sweat glands, in which morphology is parti ally mirrored by biochemical similarities, provides a perspective for class ification of problematic cases of breast-like cutaneous lesions.