Relationship between histology, development and tumorigenesis of mammary gland in female rat

Abstract

The mammary gland is a dynamic organ that undergoes structural and functional changes associated with growth, reproduction, and post-menopausal regression. The postnatal transformations of the epithelium and stromal cells of the mammary gland may contribute to its susceptibility to carcinogenesis. The increased cancer incidence in mammary glands of humans and similarly of rodents in association with their development is believed to be partly explained by proliferative activity together with lesser degree of differentiation, but it is not completely understood how the virgin gland retains its higher susceptibility to carcinogenesis. During its developmental cycle, the mammary gland displays many of the properties associated with breast cancer. An early first full-term pregnancy may have a protective effect. Rodent models are useful for investigating potential breast carcinogens. The purpose of this review is to help recognizing histological appearance of the epithelium and the stroma of the normal mammary gland in rats, and throughout its development in relation to tumorigenic potential.

Fig. 1.

Non lactating mammary gland of adult female rat. Duct (arrow) and terminal duct lobular units (arrowheads) surrounded by layer of eosinophilic connective tissue stroma embedded in adipous tissue. Hematoxylin and eosin staining (HE). Bar=20 µm.

Fig. 2.

Lymphatic follicle and lymphatics (arrow) in the lactating mammary gland (HE). Bar=20 µm.

Fig. 3.

Highly proliferative TEB with mitotic figures (arrow) in mammary gland of 14 days old female rat (HE). Bar=10 µm.

Fig. 4.

The lactiferous duct (arrow) near the base of the nipple in mammary gland of 14 days old female rat (HE). Bar=20 µm.

Fig. 5.

Groving and bifurcation of TEB (arrow) in mammary gland of 14 days old female rat (HE). Bar=20 µm.

Fig. 6.

Apocrine secretion (arrows) in lactating gland (HE). Bar=10 µm.