OBJECTIVETo investigate the correlation of the apparent diffusion coefficient (ADC) on diffusion-weighted MRI (DWI) with the prognosis of locally advanced gastric carcinoma after neoadjuvant chemotherapy (NACT).

METHODSPatients with locally advanced gastric carcinoma undergoing NACT in our hospital from November 2010 to September 2011 were enrolled in this prospective study. MRI examinations were performed before and after NACT. ADCs of the whole lesion (ADCentire) and high signal area on DWI (ADCmin) were calculated, and the cancer thickness on T2-weighted images was measured. All the patients were divided into long-term survival group and poor prognosis group, according to the 3-year survival status. The pre-therapy baseline values and early percentage changes (%delta) of the above parameters were compared between the two groups. Receiver operating characteristics (ROC) curves were employed to compare the performance of the above parameters in the discrimination of different prognosis groups.

RESULTSA total of 24 patients were enrolled in the study. There were 14 patients of long-term survival group and 10 patients of poor prognosis group. No statistical difference in baseline ADCmin and ADCentire was shown between long-term survival group and poor prognosis group [ADCmin: (1.17 ± 0.23)×10⁻³ mm²/s vs. (1.23 ± 0.27) × 10⁻³ mm²/s, P>0.05; ADCentire: (1.43 ± 0.20) × 10⁻³ mm²/s vs. (1.50 ± 0.24) × 10⁻³ mm²/s, P>0.05]. The % ΔADCmin and % ΔADCentire were both higher in long-term survival group than those in poor prognosis group (% ΔADCmin: 21% vs. 5%, P=0.06; % ΔADCentire: 23% vs. 1%, P=0.02). Through ROC curves, the AUCs for pre-therapy cancer thickness, ADCmin and ADCentire were 0.693, 0.543 and 0.600 respectively, and AUCs for % deltathickness, % ΔADCmin and % ΔADCentire were 0.532, 0.729 and 0.779 respectively, in the differentiation of prognosis. Using % ΔADC≥15% to predict long-term survival, the positive predictive value (PPV) for % ΔADCmin was 81.8% and % ΔADCentire was 83.3%. Using % ΔADC ≤ 10% to predict poor prognosis, the PPV for % ΔADCmin was 63.6% and % ΔADCentire was 70.0%.

CONCLUSIONSThe change of ADC after NACT of gastric carcinoma is correlated with long-term prognosis. The significantly increased ADC is prone to signify long-term survival. ADCentire is better than ADCmin in the prognosis prediction.