PURPOSE: Midkine (MK), a heparin-binding growth factor, has an important role in cancer progression. The outcome of patients with gastrointestinal stromal tumors (GISTs) is correlated with tumor size and mitotic count. The aim of this study was to determine MK expression in GISTs. METHODS: Midkine was detected in 31 (55%) of 57 surgically resected GISTs by immunohistochemistry with a rabbit antibody against MK and peroxidase method. RESULTS: A significant worse outcome of MK-positive patients was found (P <0.05; log rank test). Multivariate Cox regression analysis showed an independent prognostic impact (relative risk for overall survival 3.64; P <0.05). Interestingly, MK expression was significantly associated with mitotic rate (P <0.05; Chi-squared test), but not with tumor size (P = 0.97). CONCLUSIONS: Taken together, MK is a prognostic marker for GIST patients. MK might also be a useful peripheral tumor marker since it can be detected in peripheral serum. Future studies should involve higher GIST patient numbers including tumor and serum samples for detection of MK.
