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Hormonal Changes in the Breast

Breast development is under the control of prolactin, GH, estrogen, progesterone, and adrenocorticoids.

Estrogen & Progesterone (Steroids)

  • Estrogen & Progesterone receptors are located in the nucleus

  • Assessment is done on ER/PR status to evaluate biologic characteristics of a breast cancer

    • If tumor is positive for ER/PR +, then can give anti-hormonal therapy (Letrozole or tamoxifen)

  • High estrogen & progesterone levels (after ovulation) = breast fullness (body is preparing for making a baby)

    • Increased lobular acini

    • Epithelial cells become vacuolated

    • Interlobular stromal edema increases

  • Decreased levels of estrogen & progesterone (menstruation)

    • Apoptosis of epithelial cells

    • Reduction in stromal edema


  • Responsible for “milk letdown”

    • Nipple stimulation causes posterior pituitary to release stored oxytocin which then causes myoepithelial cells to contract/eject milk from the nipple.


  • Responsible for breast secretory activity (lactogenic)

  • Made in anterior pituitary

  • Initial secretory products= colostrum

    • Low lipid content

    • High protein (including maternal immunoglobulins which help protect baby from infections during initial 6 months of life)


Breast Changes during pregnancy

In pregnancy, elevated prolactin, estrogen, and progesterone increase development of the tubuloalveolar glands but inhibit milk production.

Lactational Changes in the breast

Lactation occurs when estrogen and progesterone levels fall dramatically at birth while prolactin levels remain high and oxytocin levels increase to stimulate milk release. In the absence of pregnancy or suckling (active nursing), the tubuloalveolar glands regress and become inactive.

Notice the expanded and increased number of acini in the lactating breast below. Some acinar epithelial cells become vacuolated with increased secretions in anticipation of lactation.

Lactating breast- There is expansion of both size and number of lobules compared to the pre-pregnancy state. The acini dilate and cells undergo secretory changes in preparation for lactation.

Some patients may present with a mass during pregnancy or lactation. Histologic evaluation reveals abundant lactatational changes consistent with a lactational adenoma.

The following image (onlinemidwife 2012) demonstrates the complexities of hormonal response in the breast.

Hormonal response in the breast


Menopausal Changes in the Breast

After menopause, the glandular tissue largely atrophies and is replaced by fat, although some of the lactiferous ducts may remain. Notice the increased fibrous tissue



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