Sm. Corsello et al., EFFECT OF ACUTE AND CHRONIC ADMINISTRATION OF TAMOXIFEN ON GH RESPONSE TO GHRH AND ON IGF-I SERUM LEVELS IN WOMEN WITH BREAST-CANCER, European journal of endocrinology, 139(3), 1998, pp. 309-313
Tamoxifen, an estrogen antagonist, is usually employed in the treatmen
t of breast cancer. Its mechanism of action is not well known because
an antiproliferative effect of the drug has been shown also in estroge
n receptor negative tumors, most likely mediated by the inhibition of
local growth factors and particularly IGF-I. However, the action of ta
moxifen on the GH-IGF-I axis is still open to investigation, We have i
nvestigated the influence of acute and chronic treatment with tamoxife
n on GH response to GHRH and IGF-I serum levels in six postmenopausal
women with metastatic breast cancer. A GHRH test (50 mu g i.v. at time
0, GH determinations at 0, 15, 30, 60, 90 and 120 min) was performed
(a) basally, (b) 3 h after 40 mg oral administration of tamoxifen and
(c) after 8 weeks of 20 mg twice a day oral tamoxifen treatment. IGF-I
was measured basally and after chronic tamoxifen therapy. No signific
ant modifications in GH response to GHRH were observed after acute or
chronic treatment with tamoxifen vs the basal test. On the contrary, c
hronic tamoxifen treatment induced a significant decrease in serum IGF
-I levels. Basal pretreatment levels of 123 +/- 18 mu g/l were suppres
sed to 65 +/- 11 mu g/l (mean suppression 47%, P < 0.001). These preli
minary data confirm the inhibitory effect of tamoxifen on IGF-I produc
tion but seem to exclude the possibility that this effect may be due t
o an inhibition of GH secretion.