MYC Up-regulation Is a Useful Biomarker for Preoperative Neoadjuvant Chemotherapy Combined With Anti-EGFR in Liver Metastasis from Colorectal Cancer

Discussion

The NCCN guidelines 2018 suggested treatment for focal syndrome metastasis to the liver and lung according to tumors’ surgical resectability (11). The same is true for metachronous metastases. In patients receiving i) FOLFOX/XELOX/FOLFIRI±bevacizumab therapy, ii) FOLFOX/FOLFIRI±panitumumab therapy or iii) FOLFIRI±cetuximab therapy (limited to all-RAS wild-type), hepatectomy is recommended for patients with unresectable liver cancer, lung focal syndrome, or those under FOLFOXIRI treatment. This stands true if it is judged that liver resection is possible after assessing the adequacy of resection every two months.

In a consensus on the definitions of resectability proposed to the European Colorectal Metastases Treatment Group by Nordlinger et al. (12), disease is categorized as i) resectable, ii) not optimally resectable, or iii) unresectable. Not optimally resectable is defined as “difficult to resect for technical reasons, such as proximity to hepatic vein and portal vein branches” or “technically possible to resect, but oncologically problematic, due to number of liver metastases greater than four, maximum diameter 5 cm or more, synchronous liver metastases, primary lymph node metastasis positive, and high levels of tumor markers.” Chemotherapy in combination with molecular targeted drugs is recommended, followed by curative resection if a response is achieved (13).

It has been suggested that the angiogenesis inhibitor bevacizumab may be used in combination with chemotherapy to protect against chemotherapy-induced pathological changes in the hepatic parenchyma and to improve prognosis through pathological effects (14). According to a report by Ribero et al., the onset of sinusoidal dilatation was retrospectively confirmed in 105 patients undergoing hepatectomy after combination/non-combination of bevacizumab with 5-FU/oxaliplatin therapy (14). In the bevacizumab alone 27.9% cases were classified as Rubbia-Brandt Grade 2-3 compared to the 8.1% cases in the bevacizumab combined group (p=0.006). In the same report, bevacizumab was reported to suppress the onset of oxaliplatin-induced sinusoidal dilation. The combination of bevacizumab was suggested to improve the tumor cell survival rate, which is an independent prognostic factor (15).

In contrast, the anti-EGFR antibody, cetuximab, in combination with chemotherapy has been reported to increase the response rate and yield a good curative hepatectomy transition rate (16). In the report by Folprecht et al., CRC liver metastasis of ≥5 foci, which technically makes resection difficult, has been reported in unresectable CRC patients in a randomized Phase II clinical trial who underwent FOLFOX/FOLFIRI+cetuximab therapy as targets. Of the 106 patients, 53 who received FOLFOX+cetuximab therapy had a response rate of 68% and an R0 hepatectomy rate of 38%, while in 67 cases of KRAS Exon 2 wild type, the response rate was 70% and the R0 hepatectomy rate was 33%. Regarding prognosis, the median progression-free survival (PFS) time was 10.8 months in all patients. In contrast, the median overall survival in the 33 patients with KRAS Exon 2 wild type who received FOLFOX+cetuximab therapy was 33.1 months. In addition, the median PFS of 36 patients with R0 hepatectomy was 15.4 months (median recurrence-free survival after R0 hepatectomy was 9.9 months). The median overall survival was 46.7 months (16).

Therefore, the PEAK test, FIRE-3 test, and CALGB/SWOG 80405 test were performed as randomized controlled trials to compare bevacizumab and anti-EGFR antibody therapy to treat the progression of recurrent CRC (17-19). Anti-EGFR antibodies were also confirmed to have an effect on extending survival in the presence of RAS wild type. As a result of the prospective-retrospective analysis of 68 samples from these randomized controlled trials, the benefit of the anti-EGFR antibody administration could not be obtained by administering anti-VEGF antibody to which it was compared (17-19).

Recently, the multicenter, randomized phase II ATOM trial was performed to evaluate the efficacy and safety of mFOLFOX6+bevacizumab and mFOLFOX6+cetuximab in patients suffering liver-limited metastasis from wild-type all-RAS CRC (20). As assessed by the independent review committee, the median PFS for the cetuximab arm was 14.8 months [95% confidence interval (CI)=9.7-17.3 months], whereas that for the bevacizumab arm was 11.5 months (95% CI=9.2-13.3 months; log-rank p=0.33). The hazard ratio (HR) was 0.803 (95% CI=0.513-1.256) for PFS between the two arms. Median overall survival in the bevacizumab arm was 30.4 months, in the cetuximab arm it was not achieved (HR=0.827, 95% CI=0.437-1.564). The median tumor shrinkage rate at 8 weeks was 25.3% in the bevacizumab arm vs. 37.8% in the cetuximab arm. During follow up of patients treated by surgical resection of tumors with R0/R1 status, the median PFS of the bevacizumab-treated group was 6.5 months (95% CI=4.0-13.6), whereas in the cetuximab arm it was 13.8 months (95% CI=8.4–not reached), HR=0.610 (95% CI=0.298-1.245). Of the 57 tumors for which the histopathological analysis was assessable, the Grade 1b/2/3 histopathological response rate was 66.6% (20/30) in the bevacizumab arm and 92.6% (25/27) in the cetuximab arm (p=0.0229) (20).

When considering a multidisciplinary treatment strategy for liver-localized CRC (KRAS exon 2 wild type or RAS wild type) that is difficult to curatively resect at the time of the initial diagnosis, anti-VEGF antibody and anti-EGFR antibody can be used as molecular targeted drugs in combination with chemotherapy. As there is no clear evidence as to which anti-EGFR antibody drug is suitable in every case, the evidence from this study is highly valuable.

In the present study the expression of genes associated with drug resistance was evaluated with a pathway expression analysis using the RT2 Profiler PCR Array, and comparison of gene expression in primary CRC and residual metastatic liver tumors following treatment with either anti-EGFR or anti-VEGF therapies was performed. Previously, in patients who had received anti-EGFR treatment with chemotherapy, MYC expression in metastatic liver tumors was stronger compared to patients who had received anti-VEGF treatment with chemotherapy (21).

The MYC transcription factor is central to cellular growth control, cell transformation and tumorigenesis. Under homeostasis, MYC expression generally occurs in cells with a regenerative and proliferative potential. However, its overexpression directly affects malignant transformation in various cell types and is a notable characteristic in many human cancers (22). MYC regulation occurs at both the transcriptional and post-transcriptional levels and is a direct target and effector of growth-regulatory cascades, such as the EGFR pathway (23).

Bonamy et al. have reported that the MEKK1/2-ERK1/2 signaling cascade, the ultimate controller of MYC transcription factor gene expression, mediates the EGFR-dependent regulation of the human β-defensin-1 (HBD1) (24). HBD1 is an antimicrobial peptide constitutively expressed by epithelial cells at mucosal surfaces. In addition to its microbicidal properties, the loss of HBD1 expression in several cancers suggests that it may also have an anti-tumor activity (25).

The same group have also noted that the regulatory circuit of the EGFR-MEKK1/2-ERK1/2-MYC axis, which is dysregulated in many types of human cancers, is involved in controlling the constitutive expression of HBD1. Thus, MYC increases along with p53, which results in cell cycle entry and p53-dependent apoptosis (26). We hypothesized that MYC transcription may be increased in tumor specimens obtained from CRC patients and that the MEKK1/2-ERK1/2 signaling cascade may be the main pathway transducing the signal from EGFR to MYC.

Various roles are reported for MYC that include essential cofactor interactions, targeting activity, inhibition of kinase-dependent activation, targeting of druggable key downstream target gene products, and exploiting synthetic lethal interactions. On the basis of the results of the present study, we expect to be able to target MYC directly or indirectly in the future.

In conclusion, after recent updates in the clinical guidelines from Japan, the US and EU, the genomic evaluation of KRAS, NRAS, BRAF, and MSI has become essential in planning cancer treatment. However, large full-gene sequencing projects have identified additional mutations other than these hotspots. Patients who receive anti-EGFR with chemotherapy may develop tumors with superior pathway activity, such as tumors treated with oxaliplatin) in comparison to those who receive anti-VEGF therapy with chemotherapy (27). In the future, it is predicted that the MYC gene will be found to be involved in CRC liver metastasis, which may affect the use of molecular targeted drugs.