Low RASSF6 expression in pancreatic ductal adenocarcinoma is associated with poor survival

Figure 1 Representative images of chronic pancreatitis and pancreatic ductal adenocarcinoma tissues immunostained for RASSF6. Representative micrographs of RASSF6 in pancreatic ductal adenocarcinoma (PDAC) cancerous tissues or chronic pancreatitis tissues by immunohistochemistry. A: Diffused cytoplasmic RASSF6 staining in chronic pancreatitis tissues; B: Representative negative staining of RASSF6 in PDAC; C: Extremely strong RASSF6 staining in pancreas islet (black arrow); D-F: Strongly positive RASSF6 staining in PDAC; G-I: Weakly positive RASSF6 staining in PDAC. Magnifications × 100 for A, B, D, E, G and H; × 200 for C, F and I.

Figure 2 Quantitative real-time polymerase chain reaction evaluation of RASSF6 expression in pancreatic ductal adenocarcinoma tissues. A: RASSF6 mRNA levels in pancreatic ductal adenocarcinoma (PDAC) tissues were significantly decreased compared with its levels in chronic pancreatitis tissues (P < 0.001); B: Groups were made according to the immunohistochemical results, and the consistency between immunohistochemical results and PCR results was evaluated through t test. Result showed that immunohistochemical scores were in keeping with RASSF6 mRNA levels (^bP < 0.001); C, D: RASSF6 mRNA and protein expression levels were evaluated by quantitative real-time polymerase chain reaction and Western blot in 16 cases with strong RASSF6 immunohistochemical staining. Even in these PDAC tissues with strongly positive RASSF6 staining, both the mRNA expression (C: P = 0.033) and protein levels (D: P = 0.049) were still less than para-tumor tissues.

Figure 3 Survival curves of patients with pancreatic ductal adenocarcinoma in regards to RASSF6 expression. A: There was a significant correlation between RASSF6 expression levels and overall survival (P = 0.009); B: Overall survival of patients with strongly positive RASSF6 staining was significantly higher than overall survival of those whose tumor was negative (P = 0.006); C: Weakly positive staining vs negative staining (P = 0.047); D: Overall survival of patients with positive RASSF6 staining (strongly positive plus weakly positive staining) remained better than survival of patients with negative staining of RASSF6 (P = 0.004).