Colorectal Cancer (CRC) is the second leading cancer type of the estimated number of new cancer cases in 2016 in Saudi Arabis (12.6%) (Saudi Cancer registry, 2016) for both genders. According to the American Cancer Society, CRC remains one of the main causes of high rate of cancer related death in the world, regardless of the significant improvement in the prevention, screening and therapy. CRC arises due to the transformation of the normal colonic epithelium as a result of the alteration in the genetics and the epigenetics of these cells which promotes the tumor growth. The progression of the molecular level in the tumor cells will cause genetic instability and genetics defect which leads to the development of sporadic CRC. The incidence rate and the mortality of CRC differ based in etiological factors such as age, gender, genetic background and environmental factors [1] [2] [3] [4].

Approximately, 60% of CRC caries mutations in the RAS oncogene, either KRAS, NRAS or both. KRAS and NRAS play an important role in regulating many cellular functions including cellular proliferation, apoptosis, migrations and differentiation [5] [6]. The most commonly reported mutation in the KRAS gene is located on exon 2 and consequently changes the codons 12 and codon 13. Also, another frequently reported mutation in codon 16 and 146 have been reported, however, it has lower effect on the development of the tumor cells. On the other hand, the most commonly reported mutation in the NRAS gene is located in codon 61 and 12 [7] [8]. Activating mutations in the KRAS gene has been found to be predictor of response to EGFR-targeted therapies, therefore, examining the KRAS and NRAS mutations are an essential step in clinical diagnosis and proper treatment.

Most tumors are formed from clones that carry different mutations which are called Tumor Heterogeneity. This heterogeneity has significant impact on cancer development and the response to a treatment. Since next generation sequencing becomes applicable, these genetic variations or tumor heterogeneity, can be clearly identified. Also, it can reveal any co-existing mutations in different genes [6] [9]. While defining the risk mutations and treatment approach, much needs to be done to correlate these mutations with the clinicopathological outcomes. There are discrepancies in the literature regarding prognosis of KRAS mutation in colorectal cancer patients and the reports are contradictory.

To the best of our knowledge, no data has been published before concerning the effect of KRAS and NRAS mutations and their correlations with the clinicopathological variables and overall survival in Saudi patients with colon cancer.

Therefore, and to address the major gap in our knowledge of the different roles of these genetic variations and how they correlate with the pathological findings clinically, we aimed to identify the risk molecular variants and correlate them with the clinicopathological characteristics in Saudi patients with CRC. In addition, we assessed the role of these correlations in determining the prognosis, treatment personalization and overall survival.

In this study, we investigated 16 patients with CRC by applying next generation sequencing in the population of the western region of the Saudi Arabia. Due to the main aim of the study, we focused on both genes KRAS and NRAS as prognostic factors. Furthermore, we assessed the association between these KRAS and NRAS mutations with the clinicopathological features which showed significant correlations. It is worth noting that, all the cases were muted for the P53 gene. For the KRAS mutation, the frequency was 50% of our study group. Several reports, including reports from Saudi, showed that the incidence of KRAS mutation ranged from 28.1% to 56% [10] [11] [12] [13]. This is consistent with the frequency of the KRAS mutation in our study [12] [14]. For NRAS mutation, the frequency in our study group was 25% of patients which was higher comparing the ranges of the previous reports (2.2% - 7%) [14] [15]. Regardless of the small sample size in our study group, these finding are consistent due to the high accuracy of the next generation sequencing.

In this study, we found that KRAS-mutated carcinoma was significantly more common in patients who are older than 60 years. Also, it is more common in female patients than the males. These findings are similar to previous studies reported that KRAS mutation was significantly correlated with old age and it is more common in females [16] [17]. On the other hand and contradictory to our results, different studies have shown that KRAS mutations are more common in young patients, less than 50 years old, and the mutation occurrence was comparable between male and female [18].

The correlation between KRAS mutations and tumor location remains debatable. In our study group, we observed that KRAS-mutated carcinomas were more common in right colon than left colon. Numerous studies, similar to our results, have found that tumors exhibiting KRAS mutations are more frequently in the right colon area [11] [19] [20]. Others have shown the KRAS mutation does not correlate with the location of the tumor, while others have reported that KRAS mutation was significantly higher in the left-side of the colon, in disagreement with our study [12] [14].

Comparing the results of CRC patients who were non-mutated in the KRAS gene with patients who had mutations in the KRAS gene, tumors exhibited the later had significantly more mucinous differentiation and significantly associated with higher tumor grade. This finding is consistent with other studies [21] [22]. However, the correlations between KRAS mutation and Clinicopathological characteristics are inconclusive. Some studies found an association between KRAS mutation and tumor grade or stage however others did not [10] [11] [12] [16]. The discrepancy between these studies may be due to lack of clinical and histological data, as well as due to the retrospective observational methodology.

Several reports show similar clinicopathological features between patients with KRAS and NRAS mutation [14] [23]. However, in our results, we could only find that NRAS mutation was more commonly associated with distant metastasis but this association did not differ significantly between NRAS-mutated and non-mutated NRAS patients. Also, we did not find any significant difference regarding age, gender, location of the tumor, mucinous differentiation, or grade between NRAS-mutated and non-mutated patients.

Due to the tumor heterogeneity, we detected 5 patients who had more than 1 mutation, including patients with coexistence of KRAS and either NRAS or PIK3CA genes mutations. This suggests that intratumor heterogeneity does occur in KRAS and NRAS mutant CRC and confirms that CRC is formed in clones with different mutations [15] [24]. In addition, most of these mutations were missense mutations for both KRAS and NRAS genes, except for two synonymous mutations for the KRAS and one stop-gained mutation for the NRAS gene. One interesting case in this study group had a poorly differentiated tumor, mucinous histology, 5 positive lymph nodes and the patient developed lung metastasis, eventually. This case had a high number of genetic variance and was positive for mutations in these genes: NRAS, TP53, EGFR, ERBB2, PDGFRA, KIT, MET and AKT1. This high heterogeneity in this specific case with respect to these mutations might have a critical role in worsening the case scenario and it may need implications in considering the therapeutic approaches.

Patient with mutated KRAS and with mutated NRAS respond poorly to anti-EGFR treatment. De Roock et al. analyzed the role of the NRAS mutation in patients treated with Cetuximab and chemotherapy and they found that only one of the 13 patients responded to treatment and similar results were reported by Au et al. Therefore, and due to the ineffectiveness of anti-EGFR treatment in patients with NRAS mutation, the European Drug Agency does not recommend the use of anti-EGFR drugs in such patients [23] [25].

Concerning prognosis, we found that KRAS-mutated carcinomas had a significantly worse overall survival which is consistent with other published data [13] [20] [26]. On the other hand, we could not detect any correlation between NRAS mutation and overall survival.

The present study is believed to be the first to provide information on frequency and types of KRAS, NRAS, and p53 mutations in Saudi patients with CRC. However, it has some limitations although it is the first to examine the effect of the of KRAS, NRAS and P53 genes mutations on the clinicopathological findings of CRC in Saud population. The small sample size may limit the findings. This is due to the lack of funding. In addition, it is a retrospective research and selection bias inevitably exists, as well as the limited access to the data for prognosis. Given our limited sample size and data, we acknowledge that these observations are speculative. Additional studies are required to understand the correlation of the mutations in these three genes (KRAS, NRAS, and p53) with the development of CRC for better diagnosis and improve the therapeutic effect.

The authors declare no conflicts of interest regarding the publication of this paper.

Nassir, R. and Esheba, G. (2021) The Effect of KRAS and NRAS Variants on the Prognosis of Colorectal Cancer among the Western Saudi Population. Journal of Biosciences and Medicines, 9, 81-93. https://doi.org/10.4236/jbm.2021.96008