Interleukin-6 is an autocrine growth factor in human prostate cancer

Prostate cancer is the most common cancer in American men and the second le ading cause of cancer deaths in this group. We have found that interleukin (IL)-6 protein concentrations are increased similar to 18-fold in clinicall y localized prostate cancers when compared to normal prostate tissue. Norma l and neoplastic prostatic epithelial cells in culture, with the exception of LNCaP cells, secrete IL-6. Addition of exogenous IL-6 to primary epithel ial cells in culture or the LNCaP prostate cancer cell line leads to phosph orylation of Stat-3 and increases in net cell proliferation. The concentrat ion of IL-6 receptor is increased eightfold in the prostate cancer tissues and is increased in the cancer cells by immunohistochemistry. The increased expression of IL-6 receptor is correlated with increased proliferation of prostate cancer cells in vivo as assessed by Ki67 immunohistochemistry. The se findings strongly support the hypothesis that IL-6 acts as a significant autocrine growth factor in vivo for primary, androgen-dependent prostate c ancers.