Pathology

II. Response to Hormones

Objectives:

After completing this section you will be able to:

• describe the various types of inflammatory conditions that involve the breast
• indicate etiologic agents and predisposing factors
• describe clinical lesions
• describe and identify characteristic histologic features

Once formed, the lactiferous ducts and interlobular duct system are stable and unaffected by fluctuating hormone levels during the menstrual cycle, pregnancy and lactation. The TDLUs, however, are dynamic and undergo changes with alterations in hormone levels. These changes involve both the epithelium and the intralobular stroma.

Menstrual cycle

Follicular phase: During the follicular phase of the menstrual cycle, the TDLUs are at rest and do not show any growth. The intralobular stroma is dense and indistinct from the dense interlobular stroma.

Luteal phase: After ovulation, the terminal duct epithelium proliferates and the number of terminal ducts within a lobule increases and the basal epithelial cells become vacuolated. The intralobular stroma s edematous and loose and becomes distinct from the interlobular stroma. These changes manifest as progressive fullness, heaviness and tenderness of the breast.

Menses: As the levels of estrogen and progesterone fall with the onset of menstruation, there is an increase in apoptosis in the TDLU. Lymphocytes infiltrate the intralobular stroma, which becomes dense. The TDLU finally regresses to its resting appearance.

Pregnancy

During pregnancy there is a striking increase in the number of terminal ducts and the TDLUs are enlarged, in response to the rising sex hormone levels, to form the major component of the breast tissue. The intralobular and interlobular stromas become almost inapparent.

Lactation

In the lactating breast the individual terminal ducts form acini, which show epithelial vacuolization due to the presence of secretions that also fill their lumina. After lactation, the units involute and return to their old structure.

Postmenopause

After the menopause, the TDLUs atrophy due to the low trophic hormone levels so that only small residual foci remain. The lactiferous ducts and interlobular duct system remain but the interlobular stroma is reduced in amount accompanied by a relative increase in fatty tissue.