Each breast is composed of several lobes separated by connective tissue septae. The lobes and smaller lobules contain secretory cells, which are arranged in grape-like clusters and connected to lactiferous ducts. Lactiferous ducts drain to the nipple. Breast size is related primarily to the amount of fat surrounding the mammary glands, NOT to the amount of glandular tissue itself.

Growth and maturation of the breasts are controlled by estrogen and progesterone released at puberty. Following parturition, decreased estrogen/progesterone and increased prolactin stimulate the glandular epithelium of the breast to produce milk. Milk is a rich source of proteins, immunoglobulins, fat, calcium, vitamins, and sugars needed by the infant.

In this unit, we will explore primarily proliferative and neoplastic conditions affecting the breast. It is important to note that breast cancer occurs in apporximately one in nine women in North America.

Here are the Key Points:

1. Fibrocystic change of the breast may manifest as bilateral breast lumpiness and premenstrual pain. It is characterized histologically by i) cystic dilatation of terminal ducts, ii) an increase in fibrous stroma, and iii) proliferation of terminal duct epithelium.

2. Some degree of fibrocystic change occurs in 60% to 80% of women in the United States. The cause of fibrocystic change is unknown.

3. Atypical proliferative lesions of fibrocystic change increase the risk for the subsequent development of breast cancer. The risk is further increased if the woman has a first degree relative with breast cancer.

4. Fibroadenoma is the most common benign neoplasm of the breast. It is composed of epithelial and stromal elements and originates from the terminal duct lobular unit. Fibroadenomas are usually found in women between the ages of 20 and 35.

5. Breast cancer is the most common malignancy of women in the United States. The mortality from this disease is second only to that of lung cancer among women.

6. Cancers of the breast are almost all adenocarcinomas, derived from glandular epithelium of the terminal duct lobular unit. Invasive ductal carcinoma is the most common form of breast cancer. Stromal invasion by malignant cells usually incites a pronounced fibroblastic response referred to "desmoplasia".

7. The most important prognostic factor in breast cancer is stage (extent of tumor spread). In general, small breast tumors have an excellent prognosis.. Currently 7% of American women develop breast cancer by the age of 70 years, of whom one-third will die of this disease.

8. Women whose cancers possess estrogen and/or progesterone receptors have a longer disease-free survival and overall survival rate than women with early-stage cancers who are negative for these receptors.

9. Gynecomastia refers to enlargement of the adult male breast.

The following images illustrate Key Morphological Concepts:

1. This is an example of FIBROCYSTIC CHANGE of the breast. Note the blue-domed cysts. This patient was a 34-year old woman who noted a painless nodule in the upper outer quadrant of the right breast. Mamogram revealed small foci of calcification.

2. This is an example of FIBROADENOMA. The patient was a 19-year old woman who noted a subareolar mass in her left breast. On physical examination, the tumor appeared round, sharply demarcated from the surrounding apenchyma, movable, and firm.

3. This is an example of INFILTRATING DUCTAL CARCINOMA. The margins of this surgical specimen have been inked for histopathological analysis. On gross examination, infiltrating ductal carcinomas are typically firm and show irregular margins.

4. This is an example of PAGET DISEASE OF THE NIPPLE. Paget disease is a ductal carcinoma that arises in the large ducts and spreads to the skin of the nipple. On gross examination, Paget disease resembles eczema.