The prognostic values of EGFR expression and KRAS mutation in patients with synchronous or metachronous metastatic colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and the third leading cause of cancer death in the United States where an estimated 142,820 newly diagnosed cases of CRC and an estimated 50,830 cancer deaths from CRC were reported in 2013 [1]. In Taiwan, CRC is the most common cancer type, having increased rapidly in prevalence, and the third leading cause of cancer-related death as of 2012. The incidence of CRC was 32.38 per 100,000 (7,213 new diagnoses of CRC) in 2000 and 60.72 per 100,000 (14,040 new diagnoses of CRC) in 2010 [2]. In Taiwan, 5131 people died from CRC in 2012 and the death rate was 22.0 per 100,000 [2]. The prognoses of metastasis colorectal cancer (mCRC) have improved in the past decade, with the median overall survival (OS) rate increasing from 12 months to more than 24 months [3, 4]. These improvements are considered to be a result of the development of combinations of standard chemotherapy, including fluoropyrimidine/folinic acid, irinotecan (FOLFIRI), and oxaliplatin (FOLFOX), and the introduction of new targeted biological agents such as cetuximab, panitumumab, and bevacizumab.

EGFR is a 170-KDa transmembrane receptor with an intracellular tyrosine kinase domain. EGFR is a member of the ErbB receptor family. After EFGR is bounded by EGF, EFGR forms a functionally active dimer (homodimer or heterodimer) that causes phosphorylation of tyrosine kinases in the intracellular domain of EGFR. Subsequently, complex intracellular signals to the cytoplasm and then to the nucleus are triggered by this phosphorylation [5]. Two major downstream signaling pathways are mediated by EGFR: the RAS/RAF/MEK/MAPK pathway and the PI3K–Akt pathway. The functions of the EGFR/RAS/RAF/MEK/MAPK pathway are associated with gene transcription, cell-cycle progression from the G1 phase to the S phase, and cell proliferation. Moreover, the EGFR/RAS/RAF/MEK/MAPK pathway has also been reported to play a critical role in the carcinogenesis, migration, invasion, and metastasis of CRC [5]. EGFR overexpression was previously thought to be associated with more advanced disease and worse prognoses. The prognostic value of EGFR in CRC has been investigated extensively, but it remains controversial [6‐10]. Although KRAS mutation has been studied for the predictive value of tumor response to anti-EGFR treatment and also has been confirmed to be the highly predictive of resistance to anti-EGFR treatment [11‐18], the prognostic value of KRAS mutation in synchronous and metachronous mCRC remains controversial [18‐28]. Therefore, we conducted a retrospective study to evaluate the prognostic value of EGFR expression and KRAS mutation in patients with synchronous or metachronous mCRC. Synchronous metastasis was defined as metastatic disease at the time of the primary CRC diagnosis. Metachronous metastasis was defined as the absence of metastatic disease at the time of initial CRC diagnosis with metastatic disease developing more than 3 months after resection of the primary CRC.

Of the 205 patients analyzed in this study, 98 patients had metachronous and 107 had synchronous mCRC. Positive EGFR expression was found in 80.5% patients through immunohistochemical analyses. The positive rate of EGFR expression in CRC was reported to be 25% to 82% [7]. KRAS mutation status was evaluated in 205 patients and mutation was noted in 88 of those patients (42.9%), in concordance with the mutation rate of KRAS in CRC (35% to 42%) [19]. In our patients with metachronous mCRC, EGFR expression was associated with differentiation grade of the tumor, with more moderate differentiation in patients with positive EGFR expression (P = 0.028), in accordance with the report of Andreyev et al. [25]. However, the association was not noted in our synchronous mCRC patients. The association between histological grade and EGFR expression is still controversial [6‐8, 33, 34].

For the prognostic value of EGFR for patients with metachronous mCRC, we have demonstrated EGFR as an independent negative prognostic factor for OS and DFS by multivariate Cox proportional-hazards model. The Kaplan-Meier survival analysis also showed that patients with positive EGFR expression had worse OS and DFS. Galizia et al. [7] have shown that there is strong association between disease-specific survival and EGFR expression status, and a more than 10-fold risk of cancer related death in patients with positive EGFR expression compared with patients with negative EGFR expression. The difference was even stronger in patients with Duke’s C and D colon cancer than in those with Duke’s A and B colon cancer [7]. Ljuslinder et al. [6] have shown an association between worse outcomes and higher EGFR expression at invasive margin. Giralt et al. [9] evaluated the relationship between prognosis and EGFR expression in patients with locally advanced rectal cancer (LARC) receiving preoperative radiotherapy, and they found that the pathological response rate was lower in patients with positive EGFR expression than in those with negative EGFR expression. Azria et al. [10] conducted a similar study to evaluate the prognostic impact of EGFR expression on locoregional recurrence in patients with LARC receiving preoperative radiotherapy. The locoregional recurrence rate was higher in patients with EFGR extent ≧25% than in patients with EFGR ≦25% (20% vs. 7%). The locoregional recurrence-free survival rate at 2 years was 94% and 84%, respectively (P = 0.06). EFGR extent ≧25% was a significant factor for locoregional recurrence (P = 0.037; HR, 7.18; 95% CI, 1.17–46). Theodoropoulos et al. [34] reported a significant association between high EGFR expression and advanced T3 and T4 stages (P = 0.001), which implied that EGFR overexpression was associated with tumor invasion. Furthermore, they also demonstrated a trend between positive EGFR expression and poorer OS. Deng et al. [35] reported a significant association between high EGFR expression in primary tumor and poorer OS (P = 0.046); however, the association was not noted in stage IV patients, which is in agreement with our present study. The association between EFGR expression and worse survival has also been noted in other malignancies, such as gastric cancer [36, 37], esophageal cancer [38], and breast cancer [39]. In contrast, Spano et al. [8] and McKay et al. [33] reported no significant association between EGFR expression and survival.

Through the multivariate Cox proportional-hazards analyses and Kaplan-Meier survival analysis used in this study, KRAS mutation status was found not to be a significant independent prognostic factor of OS, DFS, and PFS for patients with metachronous mCRC and synchronous mCRC. Roth et al. [19] reported a mutated rate of 37% of KRAS mutation from 1299 patients with stages II and III colon cancer. No significant association between survival (OS and relapse-free survival) and KRAS mutation status was demonstrated. Moreover, no difference was noted between survival (OS and relapse-free survival) and type of KRAS mutation stratified by condon 12 and 13 in patients with stages II and III colon cancer, which is in agreement with our analyses of patients with metachronous mCRC. Rose et al. [20] assessed the survival impact of KRAS mutation status in 110 patients with metachronous and synchronous mCRC. The OS of patients with metachronous and those with synchronous mCRC was not influenced by KRAS mutation status (P = 0.55 and 0.37, respectively), which is also consistent with our present study. Three studies [21‐23] from Asia evaluating the survival impact of KRAS mutation status in CRC patients also showed that there was no prognostic value of KRAS mutation status for OS and PFS. Recently, a systemic review and meta-analysis regarding the prognostic value of KRAS mutation status demonstrated that there was no association between KRAS mutation status and the prognosis of patients with CRC [24]. In contrast, 2 large collaborative Kirsten Ras in Colorectal Cancer Collaborative Group (RASCAL) studies [25, 26] evaluated the prognostic role in CRC. It was concluded in these studies that mutated KRAS were significantly associated with an increased risk of relapse and death and a significant association between failure-free survival and G12V of mutated KRAS in Duke’s C patients. Richman et al. [27] reported similar PFS and worse OS in patients with mutated KRAS compared to patients with wild-type KRAS. Roth et al. indicated that the KRAS mutations were assessed by each referring center according to three types of methodologies, and meta-analysis results could be affected by variations between trials [19]. In a meta-analysis assessing the predictive and prognostic value of KRAS mutations in CRC patients treated with cetuximab, it was concluded that mCRC patients with mutated KRAS could have worse PFS and OS when treated with cetuximab [28].

To our best knowledge, this study is the first to evaluate the prognostic values of EGFR expression and KRAS mutation simultaneously in patients with metachronous and synchronous mCRC. However, there are some limitations to the present study. First, the present study is a single-institution retrospective study. The study’s relatively small sample size is another limitation. Third, the KRAS mutation status was evaluated only as wild-type and mutant (codon 12 and codon 13) and we did not analyze other rare mutation types.