Background: Interleukin (IL)-6 plays a central role as a differentiation and growth factor of tumor cells. It may be hypothesized that increased serum IL-6 derives from the tumor tissue, and that serum IL-6 levels consequently reflect the biologic characteristics of the tumor. The authors investigated the association between the serum levels of IL-6 in colorectal carcinoma patients and the biologic characteristics of the tumor as well as clinicopathologic status of the patients.
Methods: Serum and tissue levels of IL-6 in 70 patients were determined using an immunoradiometric assay. Expression of IL-6 and IL-6 receptor were evaluated immunohistochemically. The proliferative activity of the tumor was assessed by nuclear Ki-67 labeling index.
Results: The concentration of serum IL-6 in the patients was significantly higher than that in normal controls. The tissue concentration of IL-6 in tumor tissue was significantly higher than that in normal mucosa, and was correlated strongly with the serum IL-6 concentration. The serum IL-6 concentration was correlated with clinicopathologic parameters, including liver metastases and tumor size, and with proliferative activity of the tumor as assessed by the Ki-67 labeling index. In the patients with Stage I or II tumors, the preoperative serum IL-6 concentration was reduced significantly 3 months after surgery. Immunohistochemically, tumor tissues that expressed IL-6 immunoreactivity had a higher incidence of expression of IL-6 receptor immunoreactivity. CONCLUSIONS. Serum IL-6 concentration reflects IL-6 concentration in the tumor component and may reflect the proliferative activity of the tumor in patients with colorectal carcinoma.