Abstract: Objective: To investigate the value of quantitative detection of insulin-like growth factor-1 (IGF-1) in the diagnosis of breast cancer. Methods: The serum IGF-1 level in 45 cases of breast cancer, 20 cases of benign breast disease and 20 healthy controls was determined by immunoradiometric assay. Results: IGF-1 levels were significantly higher in breast cancer cases than in the healthy controls and the cases of benign breast disease (P<0.01). No significant difference was found in the serum level of IGF-1 between the patients with benign breast disease and the healthy controls (P>0.05). All samples were classified as stage Ⅰ~Ⅱ or stage Ⅲ~Ⅳ, without or with lymphatic metastasis, and estrogen receptor nega-tive or positive. In stage Ⅲ~Ⅳcases, cases with lymphatic metastasis, and cases positive for estrogen receptor, the levels of IGF-1 were higher (P<0.01). A significant difference was found in the serum IGF-1 levels between the cases with posi-tive estrogen receptor and those with negative estrogen receptor(P<0.05). Conclusion: Quantitative determination of IGF-1is valuable and may be used for early diagnosis of breast cancer.