Changes in serum estrogen levels in women during tamoxifen therapy

Am J Surg. 1997 May;173(5):399-402. doi: 10.1016/S0002-9610(97)00072-X.


Background: Tamoxifen is considered an antiestrogen against breast cancer, yet it has known estrogenic side effects. We hypothesized that long-term administration of tamoxifen may significantly increase circulating estrogen levels in women with breast cancer.

Methods: Serum dehydroepiandrosterone (DHEA), estrone (E1), and estradiol (E2) levels were prospectively measured in 47 breast cancer patients before and during tamoxifen therapy for 2 years. Differences in baseline and peak hormone levels during treatment were compared, and significance was determined by paired Student's t test.

Results: Mean DHEA levels increased by 133% from 61 mg/L to 142 mg/L (P <0.001) and mean E2 levels increased by 239% from 28 pg/mL to 95 pg/mL (P <0.05). Mean E1 levels increased by 264% from 42 pg/mL to 153 pg/mL (P = 0.06).

Conclusions: Long-term tamoxifen therapy can be associated with increased serum levels of DHEA, E1, and E2. Elevated serum estrogens may explain tamoxifen's estrogenic effects and may represent a mechanism for the development of drug resistance.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Breast Neoplasms / blood
  • Breast Neoplasms / drug therapy*
  • Dehydroepiandrosterone / blood
  • Estradiol / blood
  • Estrogens / blood*
  • Estrone / blood
  • Female
  • Humans
  • Menopause / blood
  • Middle Aged
  • Prospective Studies
  • Tamoxifen / blood
  • Tamoxifen / therapeutic use*


  • Estrogens
  • Tamoxifen
  • Estrone
  • Dehydroepiandrosterone
  • Estradiol