Increased midkine serum levels in pediatric embryonal tumor patients

Serum levels of midkine (MK), a heparin-binding growth factor, are elevated in adult cancer patients. We analyzed sera of pediatric tumor patients in comparison to a large number of children and adolescents without malignant disease. MK was studied in sera of 152 noncancer patients and 29 embryonal tumor patients (14 nephroblastoma, 10 neuroblastoma, and 5 rhabdomyosarcoma) using an enzyme-linked immunosorbent assay. Noncancer patients underwent elective surgical procedures or suffered from an endocrinologic disease. They had no evidence of inflammation or injury. MK serum levels were significantly higher in tumor patients (median 0.621 ng/mL) than in noncancer patients. About 86% of tumor patients were identified using a cut-off value of 0.176 ng/mL. MK values did neither correlate with tumor size nor with stage or histology, but decreased in half of the nephroblastoma patients after chemotherapy and surgery. MK values were found to be elevated in only 2 out of 5 rhabdomyosarcoma patients. MK may serve as an additional marker for the detection of pediatric embryonal tumors, but its clinical relevance for the evaluation of response to therapy needs further study.