Serum midkine levels are increased in patients with various types of carcinomas

The level of expression of midkine (MK), a heparin-binding growth factor, is increased in many types of human carcinomas. An enzyme-linked immunoassay, which utilizes a combination of rabbit and chicken antibodies revealed that serum MK level in the controls (n = 135) was 0.154 +/- 0.076 (mean +/- SD) ng ml(-1)with an apparent cut-off value as 0.5 ng ml(-1). Serum MK level was significantly elevated in the cancer patients (n = 150) (P< 0.001); 87% of the patients showed levels of more than 0.5 ng ml(-1). All ten types of cancer examined showed a similar profile of serum MK level. There was no or weak correlation between C-reactive protein level, a marker of inflammation, and serum MK level. Furthermore, in case of gastric carcinoma and lung carcinoma, patients with stage I carcinoma already showed elevated serum MK levels. The present results indicated that serum MK could serve as a general tumour marker with a good potential for clinical application.