Figure 2.

c-MAF expression in clinical samples of CRC

(A) c-MAF mRNA level in human CRC tissues was significantly lower than in their pair-matched adjacent normal mucosal tissues (p = 0.045).

(B) Immunostaining of c-MAF protein in the duodenum as a positive control. Nuclear staining of c-MAF was noted in the duodenal epithelium. Scale bar: left panel, 500 μm; right panel, 50 μm.

(C) Immunostaining of c-MAF protein in normal mucosa and advanced CRC tissue; depth of invasion defined as T2 (deep or deeper than the muscularis propria). c-MAF expression was noted in the nucleus of normal epithelium and tumor cells. When the c-MAF positive staining cutoff was set at > 50%, the positive proportion in CRC tissues was significantly lower compared with normal mucosa (p < 0.05). Scale bar: 100 μm.

(D) c-MAF expression in early cancer and adjacent normal mucosa; early cancer defined as T0 and T1 (invasion into lamina propria or submucosa). Cancer cells showed low c-MAF expression, whereas normal epithelial cells had strong c-MAF staining. Scale bars: left panel, 500 μm; right panels, 100 μm. Investigation of 20 early cancer samples revealed downregulation of c-MAF at an early cancer stage (p = 0.038).

(E) Setting c-MAF expression in normal mucosa; as a basis, we divided the CRC cases into two groups: strong (tumor > normal, n = 35) and weak (tumor < normal, n = 63). The Kaplan–Meier survival curve shows better prognosis for overall survival in the strong expression group (p = 0.039; median follow-up 66.4 [range 41.2–791.8] months). Relapse-free survival was examined after exclusion of eight patients with stage IV disease, yielding a similar result (p = 0.040; median follow-up 63.5 [range 32.2–89.8] years). Statistical differences were analyzed using Student’s t test for continuous variables and the Chi-squared test for non-continuous data. Survival curves were developed with the Kaplan–Meier method and compared using the log rank test. ∗p < 0.05.