IGF-I levels positively associated with breast cancer risk

A new study found that circulating concentrations of insulin-like growth factor I are positively associated with the development of breast cancer. The association appears to be confined to estrogen-receptor-positive tumors and is not greatly modified by menopausal status or insulin-like growth factor binding protein 3.

According to the results, the 20% of women with the highest IGF-I concentrations were 28% more likely to develop breast cancer compared with the 20% of women with the lowest IGF-I concentrations. The association remained after the adjustment of IGF binding protein 3 and did not significantly fluctuate by menopausal status at blood collection.

Researchers analyzed data from 17 prospective studies conducted in a dozen countries that included about 5,000 cases and 10,000 matched controls.

After adjustment for age, IGF-I concentrations were positively associated with height and age at first pregnancy and inversely associated with age at menarche and amount of time since menopause. These associations were greater in overweight women and those who consumed moderate amounts of alcohol.

ORs varied according to estrogen-receptor status. The OR for a linear trend in IGF-I was significant for estrogen-receptor-positive tumors (OR=1.38; 95% CI, 1.14-1.68) but not estrogen-receptor-negative tumors (OR=0.8; 95% CI, 0.57-1.13; P=.007).

“The magnitude of the observed association is modest, but the true association could be substantially larger because of measurement error, and further work is needed to reliably quantify the relationship,” the researchers wrote.

They said a causal association may have important implications for prevention.

“Plasma concentrations of IGF-I are influenced by nutritional factors such as energy and protein intake, and the possibility of lowering breast cancer risk by reducing IGF-I should be explored,” the researchers wrote.

Key TJ. Lancet Oncol. 2010;doi:10.1016/S1470-2045(10)70095-4.