Re: Prospective Study of Colorectal Cancer Risk in Men and Plasma Levels of Insulin-Like Growth Factor (IGF)-I and IGF-Binding Protein-3

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We have followed with great interest the evolving evidence that circulating levels of insulin-like growth factor (IGF)-I and IGF-binding protein (IGFBP)-3 may be important predictors of risk for prostate, breast, and now colorectal cancers ( 1 , 2 ). Regarding colorectal cancer, most cancers are believed to develop from adenomatous polyps, known as the adenoma-carcinoma sequence ( 3 ). This sequence led us to investigate prospectively the relationship between serum IGF-I and IGFBP-3 and the presence of adenoma—as a surrogate marker of colorectal cancer risk—in an age-defined population (healthy 55- to 64-year-old males and females) undergoing flexible sigmoidoscopy screening. Three-hundred seventy-four individuals were enrolled, among whom adenomas were found in 56 (15%). Blood was taken at the time of endoscopy. Serum IGF-I was measured, after acid-alcohol extraction, by radioimmunoasay with the use of a polyclonal rabbit antihuman serum ( 4 ), and serum IGFBP-3 was determined with the use of an immunoradiometric assay with reagents from Diagnostic Systems Laboratory (Houston, TX). The statistical analysis was performed in a similar manner to that used in the report by Ma et al. ( 1 ).