MicroRNA-21 ISH analysis to predict DFS in pancreatic cancer patients undergoing adjuvant gemcitabine after curative surgery.

Abstract

234 Background: Overexpression of microRNA-21(miR-21) in pancreatic cancer has been reported to be associated with tumor cell proliferation, invasion, and also resistance to gemcitabine (GEM) chemotherapy. The aim of this study was to evaluate whether miR-21 expression, determined by microRNA ISH, was associated with clinical outcomes of pancreatic cancer patients who underwent adjuvant gemcitabine chemotherapy after curative surgery. Methods: Expression levels of miR-21 were semi quantitatively analyzed for staining intensity and distribution of positive tumor cells, by microRNA ISH in formalin-fixed paraffin embedded tissue arrays from 41 pancreatic cancer patients who underwent adjuvant GEM chemotherapy after curative resection at Kanagawa Cancer Center. The staining intensity for the miR-21 was assigned a score from 1 to 3 based on staining with1+: weakly, 2+: moderately, and 3+: strongly positive. The percentage of positive tumor cells was scored as follows, 1+: < 50% positive cells, 2+: 50-80% positive cells, and 3+: ³a 81% positive cells. A composite score was obtained by calculating the sum of these two scores. Results: 27 patients were assigned to low miR-21 expression group (score <4) and 14 patients to high miR-21 group (score 4,5,6). High miR-21 expression group had a significantly shorter DFS (P = 0.039, by log-rank test). The median DFS was 9.8 months (95% CI, 6.9-12.6) in the low miR-21 group, and 7.9 months (95% CI, 6.1-9.8) in the high miR-21 group. The median OS was 19.6 months (95% CI, 6.3-32.8) in the low miR-21 group, and 15.1 months (95% CI, 11.7-18.5) in the high miR-21 group, but was not significant. Multivariate analysis including miR-21 expression, microscopic lymphatic invasion and microscopic perineural invasion, indicated that miR-21 expression (p = 0.024) and microscopic lymphatic invasion (p = 0.035) were the independent predictor for DFS. Conclusions: A high level of miR-21 expression in pancreatic cancer was significantly associated with shorter DFS in patients who received adjuvant GEM after curative resection. miR-21 ISH analysis may serve as a significant predictor for GEM resistance in adjuvant setting.