Heterogeneous STAT1 expression in ESCC. (A) By immunohistochemistry applied to formalin-fixed paraffin-embedded tissues, variable levels of STAT1 were detectable in most ESCC tumors examined. The staining was predominantly cytoplasmic. Based on the staining intensity, tumors in our cohort was categorized into STAT1-strong (a) or STAT1-weak (b); 8 cases were STAT1-negative (c) (IHC stain, scale bar, 20 μm). Nuclear staining of STAT1 was detected in some ESCC cases (d) (IHC stain, scale bar, 50 μm). The normal epithelium (e) from a STAT1-weak tumor (shown in f) was also illustrated (scale bar, 20 μm). (B) By Western blots, STAT1 expression in ESCC tumors was examined. Compared to the benign esophageal tissue harvested at the surgical margins in the same specimens (labeled as N) cancerous tissues (labeled as Ca) often expressed a lower level of STAT1. Thus, tumors from patient #1, 2 and 4 were categorized as STAT1-low. A small subset of tumors (e.g. that from patient #3) were categorized as STAT1-high, since the expression of STAT1 in the cancerous tissue was appreciably higher than that of the benign esophageal tissues in the same specimen. (C) By Kaplan-Meier analysis, we found no significant correlation between overall survival and the expression level of STAT1, when the two groups were defined as STAT1-strong and STAT1-weak/negative (a). In contrast, we found a significant correlation between overall survival and the expression level of STAT1 protein levels when the two groups were defined as STAT1-positive or STAT1-negative (b). With the subset of patients carrying poorly or intermediate-differentiated tumors, those with STAT1-strong tumors survived significantly longer than those with STAT1-weak/negative tumors (c).