Previous studies have concluded that FAS expression played important roles in the formation of precancerous lesions, the growth, and metastasis of many human tumors including gastrointestinal cancers (Kusakabe et al., 2002). Also, VEGF was highly expressed in gastric carcinomas (Zhao et al., 2012). Because of their high expression in tumors, they constitute potential targets in cancer prevention and treatment (Butler et al., 2010).
Several studies have reported that FAS expression is elevated in primary CRC when compared with control normal mucosa (Wang et al., 2016; Zaytseva et al., 2012; Kearney et al., 2009; Visca et al., 1999). Our results revealed that FAS protein was highly expressed in 81% of our studied cases of primary CRC, which were concordant with the previous observations (Wang et al., 2016; Ogino et al., 2008; Visca et al., 2004), confirming that FAS protein plays an important role in colon carcinogenesis. Higher and lower expression of FAS were reported by others (Kearney et al., 2009; Uddin et al., 2009;Kuhajada et al., 2006; Visca et al., 1999; Rashid et al., 1997) . These discrepancies may be related to the use of different scoring systems, change in specificity and sensitivity of antibodies employed in immunohistochemistry or patient heterogeneity.
FAS expression was significantly associated with the histopathological type (p = 0.02), tumor grade (p = 0.04), and had a highly significant association with lymph node metastasis (p < 0.001) and tumor staging (p < 0.001), suggesting that this enzyme might be involved in the tumor differentiation and metastasis. These results agreed with other reports (Wang et al., 2016; Kearney et al., 2009; Ogino et al., 2008 Visca et al., 1999), however contradicted with other ones (Zaytseva et al., 2012; Uddin et al., 2009; Zhan et al., 2008;Rashid et al., 1997). In agreement with other studies (Wang et al., 2016; Visca et al., 1999; Rashid et al., 1997), increased expression of FAS was observed in mucinous carcinomas and signet ring carcinomas with the extensive metastatic involvement of lymph nodes. Therefore, FAS expression could correlate with poor prognosis of colorectal carcinoma through an association with lymph node metastases and aggressive histopathological subtypes of colorectal carcinoma. No significant association was found between FAS expression and patient age, sex and tumor site, in agreement with some studies (Wang et al., 2016; Zaytseva et al., 2012; Kearney et al., 2009; Ogino et al., 2008; Visca et al., 1999).