[Correlation of MRI apparent diffusion coeffcient with molecular marker Ki-67 in gastric cancer]

To study the correlation between MRI apparent diffusion coefficient (ADC) and expression of Ki-67 in gastric cancers, and to investigate the application of ADC value in diagnosing the malignance of gastric cancer.

A retrospective cohort analysis was performed on 87 gastric cancer patients who received MRI examination and radical resection at Zhejiang Provincial Hospital of Traditional Chinese Medicine from November 2014 to August 2015. All the postoperative resected samples were confirmed as gastric cancer. Preoperative MRI examination was performed by using Siemens 3.0-T Verio MRI with following parameters: section thickness 3 mm, gap 1 mm, matrix 182×320, field of view 40 cm. Plain scan was followed by T1-weighted fat suppression technique VIBE 3D(TR3.92/TE1.39,90degree) scans at arterial phase (the 30th second), portal venous phase (the 60th second), lag period (the 90th second), axial planes and coronal planes (the 180th second), and sagittal planes (the 210th second), respectively. ADC value of tumor was measured at b-factor of 800 s/mm² and ADC map was generated from DWI data on the work station. The expression of Ki-67 in cancer tissue was detected by routine immunohistochemical (SP) staining after surgery. Correlation between ADC value and the expression of Ki-67 in gastric cancer was analyzed.

Irregular thickening of the gastric wall and inhomogeneous enhancement of the tumor after injection of the contrast material appeared in gastric cancer. Gastric cancer tissue presented hyperintensity and normal gastric wall presented isointensity in DWI image (b=800 s/mm²). Compared with normal gastric tissue, mean ADC value of gastric cancer tissue was significant lower [(1.114±0.265)×10^-3 mm²/s vs. (2.032±0.202)×10^-3 mm²/s, t=26.209, P=0.000]. The ADC values of high-middle differentiation group, middle-low differentiation group, low differentiation group and signet ring cell carcinoma/mucinous adenocarcinoma group were (1.347±0.234)×10^-3 mm²/s, (1.179±0.257)×10^-3 mm²/s, (0.996±0.185)×10^-3 mm²/s and (1.082±0.230)×10^-3 mm²/s, respectively. The difference of mean ADC value among different tumor stages was significant(F=8.498, P=0.000). Along with the Ki-67 expression up-regulated, the ADC value decreased in cancer tissue. The Ki-67 expressions in cancer tissue was negatively correlated with cancer ADC values (r=-0.570, P=0.000). Furthermore, negative correlations of Ki-67 expressions with ADC values of high-middle differentiation group (r=-0.627, P=0.016), low differentiation group (r=-0.787, P=0.000) and signet ring cell carcinoma/mucinous adenocarcinoma group (r=-0.792, P=0.000) were observed respectively, while Ki-67 expression was not correlated with ADC value of middle-low differentiation group.

The ADC value of gastric cancer can reflect the level of tumor differentiation, and is negatively correlated with Ki-67 expression in cancer tissues.