Midkine is a serum and urinary biomarker for the detection and prognosis of non-small cell lung cancer

Abstract

Midkine, a heparin-binding growth factor, has been identified as a promising cancer biomarker. In non-small cell lung cancer (NSCLC), the serum and urine midkine levels have not been intensively investigated. The aim of the present study was to investigate the diagnostic and prognostic potential of serum and urine midkine levels in patients with NSCLC. The serum midkine levels were measured in 153 patients with NSCLC, 23 patients with benign pulmonary disease and 95 healthy controls using ELISA. Urine midkine levels were examined in 20 controls and 45 patients with NSCLC. Midkine expression in tumor tissues from 72 patients with NSCLC who underwent definitive surgical resection without any pre-operative treatments was examined by immunohistochemistry. Serum levels were significantly higher in patients with NSCLC than in healthy controls (657.36±496.58 pg/ml vs. 194.49±122.57 pg/ml, P<0.001). As shown in the ROC curve analysis, the sensitivity and specificity of the cut-off serum midkine concentration of 400 pg/ml for predicting the presence of NSCLC were 71.2% and 88.1%, respectively. Positive correlations between the serum midkine levels and immunohistochemistry staining scores (r=0.315, P=0.007) and between the serum midkine levels and urine midkine levels (r=0.636, P<0.001) were observed using Spearman's bivariate correlations. The serum midkine concentration was identified as an independent prognostic factor by multivariate analysis, and its overexpression yielded a relative risk of death of 2.072 (0.01.

Keywords: midkine; non-small cell lung cancer (NSCLC); serum biomarker; survival; urine biomarker.

Figure 1. Serum midkine concentrations in patients with NSCLC, benign pulmonary diseases and control individuals

The statistical significance of the differences was determined using the Mann-Whitney U test,*P<0.001.

Figure 2. ROC curves for patients with NSCLC and controls who did not have NSCLC

Figure 3. Representative IHC results of tumor specimens with different intensities of midkine staining

A. The mean IHC score was 0. B. The mean IHC score was 1. C. The mean IHC score was 8. D. The mean IHC score was 9.

Figure 4. Midkine immunoreactivity and serum midkine levels in 72 patients with NSCLC

The mean IHC scores and standard deviations are shown for the high-serum and low-serum midkine expression groups. The statistical significance of the differences was determined using the Mann-Whitney U test. A. Association between the serum midkine levels and immunoreactivity. The statistical significance of the differences was determined using the Spearman's correlation test (r=0.315, P=0.007). B. Serum midkine levels were significantly elevated in patients with IHC staining scores of 0 to 3 (F=4.720, P=0.005). C. and IHC proportion scores of 0 to 4 (F=4.512, P=0.003). D.

Figure 5. Relationship between the serum midkine concentrations and urine midkine concentrations in 72 NCSCLC patients

The statistical significance of the differences was determined using the Spearman's correlation test (r=0.636, P<0.0001).

Figure 6. Overall survival rate of 110 patients with NSCLC who underwent surgery

The low-serum midkine group includes patients with serum midkine levels ≤400 pg/ml (n=31). The high-serum midkine group includes patients with serum midkine levels >400 pg/ml (n=79). The statistical significance of the differences was determined using the log-rank test (P=0.004).