Apocrine epithelium of the breast: does it result from metaplasia?

Benign and malignant breast lesions may show an apocrine epithelium considered to be the result of metaplasia. In an attempt to clarify the histogenesis of the breast apocrine epithelium we searched for the presence of apocrine cells or cells with apocrine differentiation during human breast development. We analysed 10 autopsy specimens of female breasts from fetuses between 28 and 40 weeks of gestational age and tissue from 6 normal breasts, obtained after breast reduction in nulliparous young women between 22 and 28 years of age. Formalin-fixed, paraffin-embedded sections were stained with haematoxylin-eosin, PAS-diastase and a monoclonal antibody (BRST-2) anti-GCDFP-15, which is a specific apocrine marker. A 40-week fetal breast was analysed by electron microscopy. No cells with histological and ultrastructural apocrine features were found in the ducts of fetal breasts. All fetal breasts showed some ducts with sparse GCDFP-15-immunoreactive cells; the number of these cells increased with gestational age. PAS-diastase was negative. No cells with apocrine morphology were found in ducts and lobules of normal adult breasts. Scattered GCDFP-15-positive luminal epithelial cells and rare PAS-diastase-positive cells were observed in some lobules of all adult breasts. Cells with biochemical characteristics (GCDFP-15 expression) of apocrine differentiation are evident during human fetal breast development and persist in adult mammary glands. Unknown stimuli may induce these cells to take on an apocrine morphology. Apocrine epithelium of the breast may be a normal process of differentiation rather than metaplasia. We suggest the term "apocrine differentiation precursor cells" for GCDFP-15-positive breast epithelial cells with no apocrine morphology.

Clear cell hidradenoma associated with the folliculo-sebaceous-apocrine unit. Histologic study of five cases.

Hidradenomas are benign adnexal neoplasms of uncertain derivation. Although most investigators traditionally have considered these neoplasms to exhibit eccrine differentiation, with only occasional reports supporting apocrine derivation, subdivision of hidradenomas into two groups was recently suggested: those with eccrine differentiation (or poroid hidradenomas) and those exhibiting apocrine differentiation (or clear cell hidradenomas). We have observed five cases of clear cell hidradenomas manifesting unquestionable apocrine characteristics excised from sites other than the axilla, and displaying continuity with the epidermis through follicles. Because of the common embryologic derivation of apocrine glands, sebaceous glands, and hair follicles, and their histologic integration as the folliculo-sebaceous-apocrine unit, these findings suggest a possible origin of certain apocrine hidradenomas from pluripotential germinative cells present in follicles.

Development of hair coat and skin glands in fetal porcine integument.

The prenatal development of the hair coat and skin glands was studied in skin samples of ten body regions of porcine fetuses (German Landrace) ranging between 40 and 114 days (birth) of gestation (15-1000 g body weight), using light microscopy and scanning electron microscopy. During the development of hair follicles, central and lateral primary hair follicles as well as secondary hair follicles can be distinguished. Initiation of primary hair follicles begins at 40-41 days of gestational age (15 g BW) and has finished at 73 days (300 g BW). The structural development of the primary hair follicle is described in detail, and is divided into twelve stages, in general agreement with those of other mammals. The secondary hair follicles formed later remain rudimentary and disappear during the birth period. The length, depth, density and angle of slope of the primary hair follicles, and the depth of the apocrine skin glands were measured. The development of hair follicle length is closely correlated with the increase in body weight. There is a similar but changing correlation for the development of hair follicle density, especially in connection with hair follicle initiation. In the development of the apocrine skin glands, a branching of the secretory tubule is conspicuous. Secretion does not begin before birth. The development of the sebaceous glands is closely related to hair follicle maturation, i.e. the formation of the first hair canal. The results are discussed in relation to findings from corresponding studies in small laboratory animals, other domestic mammals and man.

A complex poroma-like adnexal adenoma.

Hidroacanthoma simplex, eccrine poroma, and dermal duct tumor are benign adenomas that develop from excretory ducts of eccrine glands and all three are variants of eccrine acrospiroma. To date, counterparts in apocrine or sebaceous glands have not been reported, but in this study we describe an adnexal, poroma-like adenoma that showed apocrine and sebaceous differentiations. Apocrine structures have the same embryonic origin as does the pilosebaceous system; both are derived from the primary epithelial germ. We suggest that the lesion we describe is truly a sebaceous and apocrine poroma. It must be distinguished from an infundibular adenoma whose pattern reproduces that of follicular poroma.