Does Femara cause IGF Gyno?
See my post under "Letrozole and IGF-1" for a recent study that contradicts the original study showing Femara raises IGF levels:
Letrozole is often claimed to raise IGF-1 levels based on the results of a study carried out in postmenopausal women with breast cancer (1). This result has always bothered me because IGF-1 is a potent mitogen for breast cancer cell, and this would seem to be a serious side-effect. Evidently it bothered the authors of the study too, as can be inferred from this quote taken from the study:
"This is the first report concerning the short-term effects of letrozole on components of the IGF system in breast cancer patients; further investigations are warranted in order to confirm these preliminary data."
A more recent study (2) that looked at IGF-1 levels during the administration of testosterone + letrozole offers conflicting data, apparently showing no change in IGF levels in the treatment group. Whether this is a result of the fact that the study group were hypogonadal, or a feature of letrozole, is not clear to me.
(1) J Steroid Biochem Mol Biol 1997 Nov-Dec;63(4-6):261-7
The aromatase inhibitor letrozole in advanced breast cancer: effects on serum insulin-like growth factor (IGF)-I and IGF-binding protein-3 levels.
Bajetta E, Ferrari L, Celio L, Mariani L, Miceli R, Di Leo A, Zilembo N, Buzzoni R, Spagnoli I, Martinetti A, Bichisao E, Seregni E.
(2)Eur J Endocrinol 2002 Mar;146(3):339-46
The role of sex steroids in the regulation of insulin sensitivity and serum lipid concentrations during male puberty: a prospective study with a P450-aromatase inhibitor.
Wickman S, Saukkonen T, Dunkel L.
Hospital for Children and Adolescents, University of Helsinki, PL281, FIN-00029 HUS, Helsinki, Finland.
OBJECTIVE: Our purpose was to study the sex steroid-mediated changes in serum insulin and lipid concentrations in boys during
puberty. DESIGN AND METHODS: We treated boys with constitutional delay of puberty either with testosterone plus placebo or with testosterone plus an aromatase inhibitor, letrozole, which inhibits the conversion of androgens to oestrogens. We demonstrated previously that during treatment with testosterone plus letrozole the increase in testosterone concentration was more than 5-fold higher than during treatment with testosterone plus placebo. .
The concentrations of 17beta-oestradiol, IGF-I and IGF-binding protein-3 increased during testosterone-plus-placebo treatment, but during testosterone-plus-letrozole treatment the concentrations remaine unchanged .These divergent changes in the two groups enabled us to study the effects of sex steroids and GH on insulin sensitivity and
lipid concentrations. RESULTS: The insulin concentration in the testosterone-plus-placebo-treated group did not change. In contrast, in the testosterone-plus-letrozole-treated group, the concentration decreased during letrozole treatment, indicating improved insulin sensitivity. Changes in insulin and IGF-I concentrations within 12 and 18 months were correlated. In the
testosterone-plus-placebo-treated group, the high-density lipoprotein cholesterol concentration did not change but in the
testosterone-plus-letrozole-treated group the concentration decreased. The concentrations of low-density lipoprotein cholesterol (LDL-cholesterol) and triglycerides did not change in either of the groups. CONCLUSIONS: The findings indicate that androgens do not directly alter insulin sensitivity in boys during puberty. In contrast, the observations suggest tight regulation of glucose--insulin homeostasis by GH in boys at this stage. Furthermore, our findings indicate that sex steroids do not significantly participate in the regulation of serum concentrations of LDL-cholesterol or triglycerides in boys during early and mid-puberty.
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