Diagnostic and predictive role of cell-free midkine in malignant pleural effusions

Abstract

Purpose: The detection of circulating nucleic acids has long been explored for the diagnosis and prognosis of a variety of clinical conditions. The aim of this study was to detect the cell-free mRNA expression of midkine (MK) in patients with effusions and its potential diagnostic and predictive value.

Methods: Effusions were collected prospectively from 168 patients. The cell-free RNA was extracted from effusions, and the mRNA expression of MK was detected using real-time PCR. The expression of carcinoembryonic antigen (CEA) and biochemical markers in effusions were also assayed. Primary cancer cells were isolated from the malignant effusions (n = 46). Compared with culture cell lines, the response of these cancer cells to chemotherapeutic agents was determined by CCK-8 assay.

Results: The expression of cell-free MK mRNA was significantly higher in the malignant group than in the benign group (0.13 vs 0.01, P < 0.001). The sensitivity and diagnostic accuracy of MK were 77.5 and 81.5 %, while a combination of CEA and MK reached 86.9 % sensitivity and 88.7 % accuracy. In addition, cell-free MK mRNA expression was significantly correlated with inhibitory rate of cisplatin (R = -0.72, P < 0.01).

Conclusions: Measurement of cell-free MK mRNA levels in effusion supernatant yields a high diagnostic accuracy and a potential predictive value.

Fig. 1

ROC curve for CEA (left a) and MK (right b) in effusions for distinguishing between malignant and benign effusions. The AUC of CEA and MK were 0.89 and 0.92, respectively. AUC area under the curve, ROC receiver operating characteristic, CI confidence interval

Fig. 2

Expression levels of MK in lung cancer cell lines using RT-PCR. MK was differently expressed in three lung cancer cell lines, which was highest in A549 cells and lowest in SPC-A1 cells. β-actin was used as an internal standard

Fig. 3

Correlation between cell-free mRNA expression of MK and inhibition rate of cisplatin (a), docetaxel (b) and gemcitabine (c) in primary cancer cells isolated from malignant effusion. Sensitivity of cisplatin was significantly correlated with expression of midkine. (R = −0.72, P < 0.01)