Changes in serum estrogen levels in women during tamoxifen therapy.
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.
Lum
S S
SS
Department of Surgery, Oregon Health Sciences University, Portland 97201, USA.
Woltering
E A
EA
Fletcher
W S
WS
Pommier
R F
RF
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000097:blood / Q000188:drug therapy*; D003687:Dehydroepiandrosterone / Q000097:blood; D004958:Estradiol / Q000097:blood; D004967:Estrogens / Q000097:blood*; D004970:Estrone / Q000097:blood; D005260:Female; D006801:Humans; D008593:Menopause / Q000097:blood; D008875:Middle Aged; D011446:Prospective Studies; D013629:Tamoxifen / Q000097:blood / Q000627:therapeutic use*
D004967:Estrogens; D013629:Tamoxifen; D004970:Estrone; D003687:Dehydroepiandrosterone; D004958:Estradiol