Insulin-like growth factor-I (IGF-I) has mitogenic and anti-apoptotic effec
ts on breast cancer cells, Epidemiologic studies have shown that high plasm
a levels of IGF-I and low levels of IGF binding protein (BP)-3 are associat
ed with increased risk of breast cancer in premenopausal women, The actions
of ICF-I are mediated through the ICF-I receptor (IGF-IR) and are regulate
d by IGFBPs, In circulation, most of the IGF-I binds to IGFBP-3, and bindin
g of IGF-I to ICFBP-3 inhibits the actions of IGF-I. Since free IGF-I, whic
h does not bind to IGFBPs, can readily cross the endothelial barrier to int
eract with IGF-IR, circulating free IGF-I is thought to be more relevant to
the biologic activity of IGF-I, To examine the association of free IGF-I w
ith breast cancer, we compared free ICF-I levels between 40 newly diagnosed
breast cancer patients and 40 age- and race-matched healthy controls. Plas
ma levels of free IGF-I, total IGF-I and IGF-II, as well as total, intact a
nd fragment IGFBP-3, were measured using commercial immunoassay kits, The a
ssociation between IGF-I and breast cancer was examined using the condition
al logistic regression analysis. Analysis of correlation (Spearman) showed
that free IGF-I was correlated with total IGF-I and IGFBP-3 but not with IG
F-II, The odds ratios for breast cancer patients having high plasma IGF-I (
greater than or equal to median) after adjusting for menopausal status and
IGFBP-3 were 2.00 (p < = 0.376) for total IGF-I and 6.31 (p < = 0.047) for
free ICF-I, A high ratio of ICF-I to IGFBP-3 was also associated with breas
t cancer (p < 0.05). No association was found for ICF-II, nor for total, in
tact and fragment IGFBP-3, The findings of this study suggest that measurin
g free ICF-I in circulation is more useful than measuring total IGF-I with
respect to evaluation of an association between ICF-I and breast cancer ris
k. (C) 2001 Wiley-Liss, Inc.