A 38-year-old woman with a history of repeated pregnancies and lactation presents with breast tissue enlargement. Histology shows increased number of lobules and acini. Which is the most common stimulus for mammary gland hyperplasia in women of reproductive age?
A. Prolactin alone
B. Growth hormone
C. Estrogen and progesterone
D. Thyroid hormone
Explanation
Most Common Stimulus for Mammary Gland Hyperplasia
Key Point
Estrogen and progesterone are the most common and physiologic stimuli for mammary gland hyperplasia in women of reproductive age, particularly during pregnancy and the luteal phase of the menstrual cycle.
Hormonal Control of Breast Tissue Growth
Estrogen
Effect: Stimulates ductal growth and proliferation
Receptor: Estrogen receptor (ER) on ductal epithelium
Timing: Rises in follicular phase; further elevated in pregnancy
Progesterone
Effect: Stimulates lobular and acinar development
Receptor: Progesterone receptor (PR) on lobular epithelium
Timing: Peaks in luteal phase; markedly elevated in pregnancy
Combined Action in Pregnancy
1.
First trimester: Estrogen-driven ductal proliferation
2.
Second/third trimester: Progesterone-driven acinar differentiation and lactogenic gene expression
Breast hyperplasia is estrogen and progesterone-dependent. This is why:
Breast tissue enlarges in pregnancy (both hormones ↑)
Breast swelling occurs in luteal phase (progesterone ↑)
Estrogen-blocking agents (tamoxifen) cause breast atrophy
Estrogen + progesterone replacement therapy increases breast density
Mnemonic
EPL = Estrogen, Progesterone → Lobular hyperplasia (remember: P for Progesterone → acini/lobules)
Why Other Hormones Are Not Primary Drivers
Prolactin alone: Prolactin is essential for lactation (milk synthesis) but NOT for breast tissue growth. Hyperprolactinemia causes galactorrhea, not significant breast hyperplasia. Prolactin acts after estrogen/progesterone have prepared the tissue.
Thyroid hormone & Growth hormone: These are permissive (support general metabolism and growth) but are not specific drivers of breast hyperplasia. Hypothyroidism does not prevent breast growth; growth hormone deficiency does not selectively reduce breast tissue.
Clinical Pearl
Estrogen receptor positivity (ER+) in breast cancer reflects the normal estrogen-dependence of mammary epithelium. This is why ER+ tumors respond to endocrine therapy (tamoxifen, aromatase inhibitors).
Robbins 10e Ch 3
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