BOSTON, MASSACHUSETTS. There is considerable evidence that high blood levels of insulin-like growth factor 1 (IGF-1) increases the risk of prostate and colon cancers very significantly. Now researchers at the Harvard Medical School report that high IGF-1 levels are associated with an increased risk of breast cancer in premenopausal women as well. Their study involved 32,826 female nurses aged 43 to 69 years who had blood samples taken in 1989-90. The nurses were free of breast cancer at the time of sampling but by June 1, 1994 397 of them had developed the disease. The researchers compared the plasma levels of IGF-1 and its binding protein (IGFBP-3) in blood from the 397 cancer victims with that of 620 age-matched controls. They found no difference among postmenopausal women; however, among premenopausal women younger than 50 years at the time of blood sampling they found a clear correlation between cancer incidence and IGF-1 levels. Women in the upper third of IGF-1 levels were found to have a more than seven times higher risk of developing breast cancer than women in the lower third of IGF-1 levels. This seven-fold risk increase is greater than that of most other breast cancer risk factors with the exception of a strong family history of the disease. The risk increase among all premenopausal women (irrespective of age) was 2.88 when comparing IGF-1 levels in the top tertile (upper one third) with levels in the bottom tertile. The researchers conclude that measuring IGF-1 levels may be useful in the identification of women with a high breast cancer risk. NOTE: Milk from cows treated with synthetic bovine growth hormone (BST) contains high levels of bovine IGF-1 which is identical to human IGF-1. There is growing concern that consumption of BST-milk may increase IGF-1 levels in humans.
Hankinson, Susan E., et al. Circulating concentrations of insulin-like growth factor-I and risk of breast cancer. The Lancet, Vol. 351, May 9, 1998, pp. 1393-96
Holly, Jeff. Insulin-like growth factor-I and new opportunities for cancer prevention. The Lancet, Vol. 351, May 9, 1998, pp. 1373-75 (commentary)