Background: Insulin-like growth factor-II (IGF-II) stimulates cell proliferation and is considered a potential risk factor for colorectal cancer. Tumor levels of IGF-II seem to positively correlate with colorectal cancer cell proliferation. This investigation examined the association of circulating IGF-II to the proliferating cell index (PCI) of tumor and matched normal mucosa in patients with colorectal neoplasia. Methods: Circulating IGF-II level (ng/mL) was determined in the peripheral blood plasma by ELISA. The proliferating cells in tumor or matched normal mucosa were immunohistochemically stained using the primary antibody against Ki-67. Computer image analysis was used and PCI was expressed as the percentage of Ki-67-positive cells/total counted cells. Results: Sixty-four patients were evaluated; 45 had colorectal neoplasia (27 males/18 females; mean age, 66.8 ± 11.8 years) and 19 had hyperplastic polyps (6 males and 13 females; mean age, 58.4 ± 14.4 years). Among patients with colorectal neoplasia, blood IGF-II levels were positively correlated with PCI in the matched normal mucosa (r = 0.46, P < 0.05) but not in the tumor. In patients with hyperplastic polyps, blood IGF-II levels were not correlated with the PCI in the polyps. Blood IGF-II levels were higher in colorectal cancer patients with Dukes' C/D stage (P < 0.01) or with positive lymph nodes (P < 0.01). Conclusion: Circulating IGF-II positively correlated with PCI in normal colonic mucosa of patients with colorectal neoplasia, suggesting that IGF-II may have a role in initiating the carcinogenic pathway by stimulating cell proliferation. Blood IGF-II was increased in advanced colorectal cancer, indicating that it might enhance colorectal cancer progression and be a useful marker of poor prognosis.
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