## 4 Discussion  
In this study, we investigated the associations between the expression status of SATB1, SMAD3, Erzin, \(\beta\)-catenin and clinicopathological variables, including survival outcome of PDAC patients. Importantly, we evaluated the utility of the examined factors as prognostic markers in pancreatic cancer separately and in combination. To verify the results, we complemented the protein expression data of our cohort with mRNA-seq data of PAC cases obtained from the TCGA. In addition, the protein-protein interaction (PPI) network for \(\beta\)-catenin, Erzin, SATB1, SMAD3 and their 50 neighbors was constructed and functionally annotated. In the past few years, several studies have been conducted to evaluate the expression level and role of SATB1 in many human cancers, including PDAC [32; 33; 34]. In our investigation, expression of SATB1\({}^{\text{n}}\) was significantly reduced or lost in PDAC specimens as compared to non-cancerous adjacent tissues, while SATB1\({}^{\text{c}}\) was present in the abnormal tissue, but it was not observed in any of the control samples. [PERSON] et al. revealed that SATB1 expression was significantly upregulated in pancreatic cancer specimens compared to in non-cancerous adjacent tissues [32]. However, [PERSON] et al. did not specify what type of SATB1 immunoexpression patterns they assessed, but on the representative micrograph of pancreatic cancer tissue, exclusively cytoplasmic pattern could be seen [32]. Our finding suggests that cells of the pancreatic ducts undergo a significant loss of SATB1\({}^{\text{n}}\) expression during pancreatic carcinogenesis, and this preferentially takes place in well-differentiated and moderately differentiated cancer cells than in the poorly differentiated ones. Notably, loss of SATB1\({}^{\text{n}}\) expression in PDAC specimens was associated with reduced OS (297 days vs. 561 days), but the survival difference was not statistically significant (\(p=0.118\)). On the other hand, SATB1\({}^{\text{c}}\) was only present in PDAC (30.88%) but not in the control tissue, leading us to hypothesize that this staining pattern may have a clinical meaning in PDAC. Indeed, patients with SATB1\({}^{\text{c}}\) expression had significantly shorter median OS than patients without cytoplasmic SATB1 staining (458 vs. 117 days). Furthermore, in the multivariate analysis accounting for conventional risk factors, SATB1\({}^{\text{c}}\) expression tended to be an independent prognostic factor for poor overall survival. Our study may be simply underpowered to observe statistically significant effects of SATB1 in our cohort because of the relatively small sample size and the limited number of samples overexpressing SATB1\({}^{\text{n}}\) or those exhibiting cytoplasmic SATB1 staining. Nevertheless, without reaching statistical significance in certain survival analyses, our results do not allow us to infer anything conclusively on the role of SATB1 in PDAC. However, they still raise the possibility that SATB1 may function as a tumor suppressor in at least some PDAC cases, i.e., under specific clinicopathological circumstances. SATB1 functions as a nuclear DNA-binding protein, and herein, it was SATB1's inability to fulfill its nuclear roles due to the loss of nuclear expression and/or cytoplasmic retention that correlated with a poor prognosis of PDAC patients. It is not unexpected, given that SATB1 acts as a global epigenetic and transcriptional regulator of gene expression. Thus, loss of its function may lead to widespread genomic consequences that can contribute to cancer [35]. Furthermore, in our TCGA data, high expression levels of _SATB1_ mRNA were found to predict better OS independently of age at diagnosis, tumor grade, as well as pT and pN stage. As an aside, [PERSON] et al. reported that cytoplasmic SATB1 localization in T cells could be attributed to a single point mutation at either Lyss29 or Arg32, which abrogates its nuclear localization [36]. Whether this stays true in PDAC requires additional studies.