Mammary gland

Mammary gland. The mammary glands are altered sweat glands with an apocrine type of secretion. The glandular tissue has an ectodermal origin. By the time of puberty, the mammary glands reach full development, which reaches its maximum after the first birth with a full term pregnancy. Under the influence of hormonal stimulation during pregnancy there is a gradual increase in the number of glandular lobules.

In the process of growth and development of the breast, four types of glandular lobules can form. Lobules of the first type are the least differentiated and are known as virgin lobules, since they represent an immature female breast up to the menarche. In the lobules of this type there are 6 to 11 ducts. Lobules of the second type evolve from the lobules of the first type, the glandular epithelium in them acquires a detailed morphological differentiation characteristic of glands in the reproductive age outside of pregnancy. The number of ducts also increases, respectively, about 47 per lobe.

Lobules of the third type evolve from the lobules of the second type, have an average of 80 ducts or alveoli per lobule. These lobules are already formed under the influence of hormonal stimulation during pregnancy. And, finally, the fourth type of lobules is represented in women with lactation and reflects the maximum differentiation of the glandular component and the development of mammary glands during lactation. In the lobes of this type there are about 120 channels. These lobules are not found in women who have not had a pregnancy. After the termination of a lactemia the lobules of the fourth type regress in lobules of the third type. After the onset of menopause in the mammary gland, involuntary changes occur in both women giving birth and those who have not. This is manifested by an increase in the number of lobes of the 1 st and 2 nd types. At the end of the fifth decade of life in the mammary gland of women giving birth and nulliparous women are represented mainly lobules of the 1st type.

Normally, the main tissue elements of the mammary glands, through which their role in reproductive function is realized, are represented by a combination of epithelial and stromal tissue.

Epithelial elements are represented by branching ducts, which are connected with the functional units of the gland by lobules and a nipple.

The stroma consists of a different number of fatty and fibrous connective tissues that form the very volume of the gland outside the periods of lactation.

At birth, the epithelial component of the mammary gland is represented by a small number of rudimentary ducts located deeper than the nipple-areola complex. In the prepubertal period, these ducts slowly grow and branch, accompanied by an increase in the stromal component. In the post-pubertal period, the end of the ducts form sacular buds, with the accompanying stromal growth, which increases the volume of the gland in this period. During pregnancy, many glands develop from each bud.

By the end of pregnancy, the glandular component increases to such an extent that the mammary gland consists of glandular tissue, with a small number of stroma.

After the end of lactation, atrophy of the glandular tissue is noted and the stroma again becomes the dominant component of the mammary gland.

After the onset of menopause, atrophy of glandular components occurs with a pronounced decrease in the number of lobules to such an extent that in some regions of the glands lobules completely disappear and only ducts remain. The connective tissue component of the stroma also decreases, while the stromal fatty tissue increases in its content.

From this brief description of the changes in the epithelial and stromal elements of the mammary glands, depending on the periods of the reproductive cycle, it follows that all these rearrangements are based on physiological but multidirectional processes of proliferation and apoptosis, which in the end result in adequate changes in the structure and function of the glands in accordance with tasks in each age period of the reproductive cycle.

Benign changes in the mammary gland, in the basis of which the cell hyperplasia lies in the predominant number of cases, form a rather heterogeneous group of disorders. With regard to this pathology, the doctor usually solves two diagnostic problems: first, to exclude malignant neoplasm in the palpable formation, and secondly, when carrying out a histological examination (according to the indications) to obtain useful information on the morphological characteristics of the observed changes.

In this respect, there is a tendency to consider clinically benign changes in the mammary glands in terms of assessing the possible risk of developing a malignant process in the future (which seems to be correct). As an illustration to what has been said, it is appropriate to cite the jointly worked out decision of the "Conciliation Commission", which included forty prominent specialists of the American board of pathologists on the problem of benign breast processes (October 3-5, 1985, New York, USA). The document was based on the results of prospective observations performed by W. D. Dupont and D. L. Page (1985) in a large group of patients (1500 people). They had a biopsy for clinically benign neoplasms of the mammary glands, and their fate was traced for a considerable time.

In accordance with the results obtained, all benign changes in the mammary gland were divided into three groups according to the degree of relative risk of cancer development.

1st group. Non-proliferative processes (there is no risk of malignancy).

Cysts. Cysts arise from the final ducts of the lobes. In a typical case, the epithelium consists of two layers: the inner epithelial layer and the outer one, represented by myoepithelial cells. In some cysts, the epithelium may be thinned or absent. In other cases, apocrine metaplasia is observed in the epithelium. Cysts often contain an amorphous protein secret.

Apocrine metaplasia. These changes in the epithelium of the mammary gland are characterized by the transition of cuboidal cells into cylindrical cells, in which round nuclei are identified, with abundant eosinophilic cytoplasm and apocrine secretion.

Moderate hyperplasia of the epithelial lining of the ducts. It is characterized by an increase in the number of epithelial cells in the ducts of more than two cells in the thickness of the duct, but not more than four. The epithelial cells do not overlap the lumen of the duct.

Fibroadenoma. The tumor is well delimited from surrounding tissues, consists of benign epithelial and stromal elements.

2nd group. Proliferative processes without atypia (insignificantly increased risk of malignancy, in 1,5-2,0 times).

Moderate or severe hyperplasia. Characterized by the fact that the epithelial cells fill the lumen of the duct and even expand it. Kernels vary in shape, size and orientation. The remaining free spaces of the ducts also vary in size and shape.

Intra-flow papilloma. The intraprostatic lumen is papilliform. At high magnification, it can be seen that the papilla consists of a fibrovascular core (core), which is covered with two layers of epithelial cells: the epithelial layer adjacent to the duct lumen and the myoepithelial layer lying on the papilla core.

Sclerosing adenosis. It is represented by proliferation of glandular structures and stroma, located in the center of the lobule of the breast. These glands can be squeezed and change shape due to fibrous stroma, sometimes forming a picture of "cancer with infiltrative growth."

3rd group. Atypical hyperplasia is a moderately increased risk of malignancy (4-5 times).

Protocol atypical hyperplasia. This kind of epithelial structure has some, but not all, signs of protocol cancer in situ. Near the center of the duct, a population of relatively round identical epithelial cells is determined, with regularly located nuclei. Closer to the periphery of the duct, the epithelial cells retain their orientation. There are variations in the size and shape of the intracapsular spaces that remain, as there are signs of intermediate between the cancer in situ and ductal hyperplasia. These changes are referred to as "atypical ductal hyperplasia."

Lobular atypical hyperplasia. This lesion is characterized by the proliferation of small identical cells in the acini, which are not stretched by them. Since this type of proliferation has some but not all features of lobular carcinoma in situ, these changes are qualified as "atypical lobular hyperplasia".

As can be seen from the presented data, the panel of qualified pathologists, based on the results obtained during the morphological study of the biopsy material of the mammary glands, concluded that epithelial hyperplasia could be classified as a risk of malignant transformation of the mammary epithelium.

At the same time, the lacrimal ducts of different levels of branching, but having an epithelial lining in not more than two layers, carry no risk. With mild, moderate or severe hyperplasia of the ductal epithelium, in the absence of signs of atypical hyperplasia, these types of proliferation do not carry significant risks of malignancy.

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