The occurrence and development of CRC metastases involve a number of signalling pathways, such as transforming growth factor β (TGF-β), Wnt, Notch, Hedgehog, phosphatidylinositol 3-kinase and protein kinase B (PI3K/Akt), nuclear factor kappa light chain enhancer of activated B cells (NF- κB) and microtubule associated protein kinase (MAPK) . KRAS mutation is the most common mutated driver gene in CRC, with an incidence of approximately 40% [29, 30]. Our study showed the incidence of total RAS mutations in 26.0% of IU-CRLM patients. There was a significant association between RAS mutation and early progression of CRLM after first-line systemic therapy. The results indicated that RAS mutation IU-CRLM represented more malignant biological behaviour than RAS wild-type IU-CRLM.
The epidermal growth factor receptor (EGFR) signalling pathway, which is activated by mutated KRAS, plays a crucial role in CRLM progression. In the EGFR pathway, the RAS protein acts as a gating switch, and the activation of RAS and MEK, downstream molecules of the RAS protein, depends on RAS mutation. Once RAS is mutated, it will constantly activate downstream pathways involving MAPK and PI3K-AKT as well as the downstream transcription factors of these pathways. Ultimately, mutated RAS regulates the expression level of proteins related to tumour invasion and metastasis. [31, 32] Animal experiments also confirmed that CRC with mutated KRAS could promote the occurrence of lung metastasis with cells from liver metastases by activating the MAPK pathway.  These results suggest that KRAS mutation enhances malignant invasion and metastasis in CRC cells, which accelerates the progression of CRLM. In addition, glycolysis metabolism in cancer cells is elevated by mutated KRAS.  Previous studies reported that KRAS mutation was able to upregulate the expression levels of GLUT1, HK and LDH, which increased the process of tumour glucose uptake. Recently, research from Yun et al. revealed an increase in the expression level of GLUT1 and higher glucose uptake in CRC cell lines with mutated KRAS [35, 36]. Such alterations in metabolism confer CRC cells with a survival advantage, as they can gain long-term survival advantages in low-glucose environments, thereby creating favourable conditions for tumour metastasis.
Interestingly, our results showed that RAS mutation was a risk factor for early progression only in patients with successful conversion therapy outcomes. In fact, in recent years, a growing number of studies have indicated that RAS mutation is a negative prognostic factor for patients with CRLM after surgery. A phase II clinical study from the Medical University of Vienna enrolled 60 patients with initially resectable CRLM, all of whom had been administered oxaliplatin combined with bevacizumab before hepatectomy. The results demonstrated that in patients with KRAS mutations, the overall survival (OS) and relapse-free survival (RFS) were shorter.  Another study from the M.D. Anderson Cancer Center enrolled a total of 524 CRLM patients who underwent both curative liver section and RAS mutant detection. The results suggested that the median overall survival was remarkably shorter in patients with KRAS codons 12 and 13 mutations than in wild-type patients.  A study conducted by Brudvik KW et al indicated that although the size of tumours was similar, liver metastases with mutational KRAS infiltrated more widely than wild-type metastases, increasing the rate of margin positivity, which may be the leading cause of poor prognosis. 
However, in patients experiencing conversion therapy failure, tumours may develop acquired resistance during treatment. At present, one of the mechanisms of acquired resistance is secondary mutations in driver genes. In metastatic CRC, gene mutations in RAS/RAF pathways are the most common molecular mechanism causing acquired resistance.  Calcagno SR et al found that KRAS G12D mutation could promote proliferation of the intestinal epithelium by constantly activating the MEK-ERK signalling axis in the mouse intestinal epithelium. The results of this study showed that mutations in KRAS and aberrant activation of its downstream signalling pathway participated in the development of acquired resistance in CRC.  Since our study failed to conduct dynamic circulating tumour DNA detection, RAS status before first-line systemic therapy may not accurately predict early progression in patients with secondary mutations.
Moreover, in our study, the early progression rate of patients with successful conversion therapy was significantly decreased compared with that of patients experiencing therapy failure. For patients with RAS mutations, the current guidelines recommend that if patients can tolerate treatment, FOLFOXIRI combined with bevacizumab can maximize the efficacy of conversion therapy . Additionally, surgeons should ensure adequate liver resection to reduce the rates of positive surgical margins in these patients. Meanwhile, a sufficient number of preoperative chemotherapy cycles and more frequent postoperative follow-up visits may effectively prevent early disease progression.
There are some limitations to this retrospective study. First, the number of included patients may be inadequate, and selection bias may exist. Hence, larger numbers of patients are required for external validation. Second, several biomarkers were identified as crucial prognostic factors for survival and recurrence, including BRAF, PI3K and TP53, which are still under debate [40–42]. In this study, we included only RAS in the analysis; future studies should take more gene status into consideration to gain a better understanding of the influence of these biomarkers on early disease progression. The 5-year survival data were unavailable for some patients due to an insufficient follow-up duration. This issue may have led to the underestimation or overestimation of the effect of RAS mutation on conversion therapy outcomes.