PU.1 is a nuclear factor of immunocompetent cells of tumor stroma in colorectal cancer

Introduction. Tumor-associated macrophages (TAMs) are traditionally considered to be a pro-tumor fac-tor that promotes the growth of various tumors; however, for colorectal carcinomas (CRC), the prognostic significance of TAMs has not been fully determined, which may be due to the lack of macrophage markers suitable for this tumor type. The aim of this work was to study the expression of the nuclear marker of stromal cells PU.1 in colorectal tumors and its association with the clinical and morphological tumor characteristics. Materials and methods. We performed an immunohistochemical analysis to assess the expression of PU.1, CD68, and CD20 in 85 primary CRCs. The Mann-Whitney test was used to determine statistically significant differences in independent groups. Correlation analysis of the expression of the studied protein was carried out by determining the Spearman’s rank correlation coefficient. Differences were considered statistically significant at p <0.05. Results. We analyzed the expression of PU.1, CD68, and CD20 in CRC and detected positive PU.1 and CD68 expressions in tumor stromal cells in all of the studied samples. Expression of CD20 was observed in 87% of cases. We showed that in colorectal tumors all CD68+ or CD20+ cells express PU.1 and that PU.1 and CD20 were significantly associated with the disease stage (p=0.036 and p=0.002) and the presence or absence of regional metastases (p=0.022 and p=0.007). In addition, PU.1 showed a significant correlation with the distant metastases’ presence and tumor localization (p=0.031 and p=0.022). Higher content of PU.1 was typical for colon tumors without metastases. CD20 also showed a significant association with tumor size (p=0.025). No significant correlations with clinical and morphological features were found for CD68. We also demonstrated that the number of PU.1+ cells in tumors significantly positively correlates with CD68 (r=0.231, p=0.036) and CD20 (r=0.267, p=0.015). Conclusion. The results of this study indicate that PU.1 can be considered as an independent marker of a favorable prognosis in CRC patients. Keywords: colorectal cancer, expression, CD20, CD68, PU.1, macrophages, B-cells