Influence of tamoxifen on plasma levels of insulin-like growth factor I and insulin-like growth factor binding protein I in breast cancer patients.
Plasma levels of insulin-like growth factor I (IGF-I) and insulin-like growth factor binding protein I (IGFBP-I) were measured in fasting blood samples obtained from 16 postmenopausal breast cancer patients before and during tamoxifen treatment for 1 to 6 months. Tamoxifen suppressed total plasma IGF-I by a mean of 28.5% (P less than 0.001) but elevated plasma IGFBP-I by a mean value of 78% (P less than 0.001). Changes in plasma levels of growth hormone, insulin, or insulin C-peptide were not observed. These findings suggest that tamoxifen exerts its influence on plasma IGF-I and IGFBP-I by mechanisms other than those known to regulate the plasma levels of these peptides, primarily growth hormone and insulin, respectively. A dual effect suppressing plasma IGF-I and elevating plasma IGFBP-I suggests that tamoxifen may have a significant influence on endocrine and possibly paracrine delivery of IGF-I to breast cancer cells in vivo.
Lønning
P E
PE
Department of Oncology, Haukeland University Hospital, Bergen, Norway.
Hall
K
K
Aakvaag
A
A
Lien
E A
EA
D000368:Aged; D001943:Breast Neoplasms / Q000097:blood* / Q000188:drug therapy; D002352:Carrier Proteins / Q000097:blood*; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008875:Middle Aged; D013629:Tamoxifen / Q000494:pharmacology* / Q000627:therapeutic use; D013997:Time Factors
D002352:Carrier Proteins; D018970:Insulin-Like Growth Factor Binding Protein 1; D013629:Tamoxifen; D007334:Insulin-Like Growth Factor I