Analysis of HER-3, insulin growth factor-1, nuclear factor-kB and epidermal growth factor receptor gene copy number in the prediction of clinical outcome for K-RAS wild-type colorectal cancer patients receiving irinotecan-cetuximab

Prognostic and predictive biomarkers for anti-EGFR monoclonal antibody therapy in RAS wild-type metastatic colorectal cancer: a systematic review and meta-analysis

BACKGROUND

RAS mutations affect prognosis in patients with metastatic colorectal cancer (mCRC) and have been identified as strong negative predictive markers for anti-epidermal growth factor receptor monoclonal antibody (anti-EGFR mAb) therapy, but many tumors containing wild-type RAS genes still do not respond to these therapies. Some additional biomarkers may have prognostic or predictive roles, but conclusions remain controversial.

METHODS

We performed a meta-analysis and systematic review of randomized controlled trials comparing anti-EGFR mAb therapy with alternative therapy that investigated the prognostic and predictive impact of additional biomarkers in RAS wild-type (wt) mCRC patients. Hazard ratios (HRs) and 95% confidence intervals (CIs) for progression-free survival (PFS) and overall survival (OS) and odds ratios (ORs) for objective response rate (ORR) were calculated. The prognostic value of biomarkers was investigated by separately pooling HR and OR for different treatment groups in an individual study. The predictive value was assessed by pooling study interactions between treatment effects and biomarker subgroups.

RESULTS

Thirty publications reporting on eighteen trials were selected, including a total of 13,507 patients. In prognostic analysis, BRAF mutations were associated with poorer PFS [HRs = 3.76 (2.47-5.73) and 2.69 (1.82-3.98)] and OS [HRs = 2.66 (1.95-3.65) and 2.45 (1.55-3.88)] in both the experimental and control arms; low miR-31-3p expression appeared to have longer PFS and OS. In terms of predictive effect, a lack of response to anti-EGFR therapy was observed in patients with BRAF mutant tumors (Pinteraction < 0.01 for PFS). Patients with tumors with any mutation in the KRAS/NRAS/BRAF/PIK3CA gene also showed similar results compared with all wild-type tumors (Pinteraction for PFS, OS, and ORR were < 0.01, < 0.01 and 0.01, respectively). While low miR-31-3p expression could predict PFS (Pinteraction = 0.01) and OS (Pinteraction = 0.04) benefit. The prognostic and predictive value regarding PIK3CA mutations, PTEN mutations or deletions, EGFR, EREG/AREG, HER2, HER3, and HER4 expression remains uncertain.

CONCLUSIONS

In RAS wt mCRC patients receiving EGFR-targeted therapy, BRAF mutation is a powerful prognostic and therapy-predictive biomarker, with no effect found for PIK3CA mutation, PTEN mutation or deletion, but the combined biomarker KRAS/NRAS/BRAF/PIK3CA mutations predict resistance to anti-EGFR therapy. Low miR-31-3p expression may have positive prognostic and therapy predictive effects. Evidence on the prognostic and predictive roles of EGFR and its ligands, and HER2/3/4 is insufficient.

The prognostic role of HIF-1α and NF-κB expression in RAS wild-type metastatic colorectal cancer: A Turkish Oncology Group (TOG) study

BACKGROUND

Not all RAS wild-type metastatic colorectal cancer (mCRC) patients experience the same benefit from anti-epidermal growth factor receptor (EGFR) treatments. Studies have shown that nuclear factor-κB (NF-κB), hypoxia-inducible factor-1α (HIF-1α), interleukin 8 (IL-8) and transforming growth factor β (TGF-β) may be therapeutic targets for mCRC. The aim of this study was to clarify the prognostic value of NF-κB, HIF-1α, IL-8, and TGF-β expression in patients with left-sided mCRC receiving EGFR inhibitors.

METHODS

Patients with RAS wild-type, left-sided mCRC treated with anti-EGFR on the first line between September 2013 and April 2022 were included. Immunohistochemical staining for NF-κB, HIF-1α, IL-8 and TGF-β was performed from tumor tissues of 88 patients. Patients were divided into NF-κB, HIF-1α, IL-8 and TGF-β expression positive and negative group, moreover, expression positive group were also divided into two group as expression intensity low and high group. The median follow-up was 25.2 months.

RESULTS

Median progression-free survival (PFS) was 8.1 (6-10.2) months in the cetuximab group, 11.3 (8.5-14) months in the panitumumab group (p = 0.09). Median overall survival (OS) was 23.9 (4.3-43.4) months in the cetuximab group, 26.9 (15.9-31.9) months in the panitumumab group (p = 0.8). Cytoplasmic NF-κB expression was present in all patients. The mOS was 19.8 (11-28.6) months in NF-κB expression intensity low group and 36.5 (20.1-52.8) months in high group (p = 0.03). The mOS of the HIF-1α expression negative group was significantly longer compared with expression positive group (p = 0.014). There was no significant difference in IL-8 and TGF-β expression status on mOS and mPFS (for all, p > 0.05). Positive expression of HIF-1α was poor prognostic for mOS in the univariate analysis (HR:2.7, 95% CI 1.18-6.52, p = 0.02) and in multivariate analysis (HR 3.69, 95% CI 1.41-9.6, p = 0.008). High cytoplasmic expression intensity of NF-κB was found to have a good prognostic value for mOS (HR 0.47, 95% CI 0.26-0.85, p = 0.01).

CONCLUSION

High cytoplasmic expression intensity of NF-κB and negative expression of HIF-1α could be a good prognostic marker for mOS in RAS wild-type left-sided mCRC.

Drug Resistance in Colorectal Cancer: From Mechanism to Clinic

Colorectal cancer (CRC) is one of the leading causes of death worldwide. The 5-year survival rate is 90% for patients with early CRC, 70% for patients with locally advanced CRC, and 15% for patients with metastatic CRC (mCRC). In fact, most CRC patients are at an advanced stage at the time of diagnosis. Although chemotherapy, molecularly targeted therapy and immunotherapy have significantly improved patient survival, some patients are initially insensitive to these drugs or initially sensitive but quickly become insensitive, and the emergence of such primary and secondary drug resistance is a significant clinical challenge. The most direct cause of resistance is the aberrant anti-tumor drug metabolism, transportation or target. With more in-depth research, it is found that cell death pathways, carcinogenic signals, compensation feedback loop signal pathways and tumor immune microenvironment also play essential roles in the drug resistance mechanism. Here, we assess the current major mechanisms of CRC resistance and describe potential therapeutic interventions.

Retrospective Comparative Analysis of KRAS G12C vs. Other KRAS Mutations in mCRC Patients Treated With First-Line Chemotherapy Doublet + Bevacizumab

Background

KRAS mutations in metastatic colorectal cancer (mCRC) define a subset of tumors that have primary resistance to anti-EGFR-based therapy. Data concerning whether different KRAS mutations may also have a prognostic value are lacking. Furthermore, novel KRAS G12C inhibitors are currently in development. The aim of our analysis was to compare response rates in patients treated with first-line chemotherapy doublet + Bevacizumab among different KRAS variants. Secondary end-points were progression free survival (PFS) and overall survival (OS).

Methods

Patients with KRAS mutated mCRC treated with either FOLFIRI/FOLFOX/XELOX + Bevacizumab were eligible for enrollment. Patients whose tumor harbored NRAS mutations or that coexpressed also BRAF mutations were excluded from this retrospective analysis. Patients’ individual data were collected from patients’ records. Propensity score matching (nearest method, 1:2 ratio) was used to define the two different groups of patients for comparison (KRAS G12C mutated vs other KRAS variants). Eastern Cooperative Oncology Group Performance Status (ECOG PS), sex, metastatic site of involvement, synchronous vs metachronous metastatic disease, tumor sidedness, mucinous histology, primary tumor surgery, more than two lines of treatment for metastatic disease, and radical surgery of metastases were used as matching factors. Response rate (RR) was calculated by RECIST 1.1 criteria. Both progression free-survival and overall survival were calculated by Kaplan–Meier method. Categorical variables were compared by Fisher exact test for binomial variables and by chi-square test for all other instances. The level of statistical significance p was set at 0.05 for all tests.

Results

A total of 120 patients were assessed in the final analysis. Out of the 120 patients, 15 (12%) were KRAS G12C mutated. In the whole cohort of patients, 59/120 (49%) had partial response (PR), 42/120 (35%) had stable disease (SD), and 19/120 (16%) had progressive disease (PD) as the best response. In KRAS G12C patients, 4/15 (27%) had PR, 6/15 (40%) had SD, and the remaining 5/15 (33%) had PD as the best response. In patients with other KRAS mutations, 55/105 (52%) had PR, 37/105 (35%) had SD, and the remaining 13/105 (12%) had PD as the best response. The difference in RR between the two groups of patients was statistically significant (p=0.017). On the other hand, no difference in PFS (p=0.76) and OS (p=0.56) was observed. After matching procedures, the difference in response rates between KRAS G12C mutated patients vs the matched cohort of patients with other KRAS mutations remained statistically significant (p=0.016). KRAS G12C mutations were not associated with differences in sites of metastatic involvement, sex, and ECOG PS. On the other hand, synchronous vs metachronous metastatic disease (p=0.039), age > 75 years (p=0.043), and mucinous histology (p=0.008) were more frequent in G12C mutated tumors.

Conclusions

In our cohort of patients, it was observed that KRAS G12C mutations are associated with worse response rates compared to other KRAS variants when treated with standard chemotherapy doublet + Bevacizumab. On the other hand, both PFS and OS were not significantly different. Based on these findings, we believe that new treatment options focused on KRAS G12C inhibition should be tested mainly in first-line setting and in addition to standard chemotherapy doublet + Bevacizumab for mCRC patients, as they might “fill the gap” in response rates that was seen in our study.

Precision oncology in metastatic colorectal cancer - from biology to medicine

Remarkable progress has been made in the development of biomarker-driven targeted therapies for patients with multiple cancer types, including melanoma, breast and lung tumours, although precision oncology for patients with colorectal cancer (CRC) continues to lag behind. Nonetheless, the availability of patient-derived CRC models coupled with in vitro and in vivo pharmacological and functional analyses over the past decade has finally led to advances in the field. Gene-specific alterations are not the only determinants that can successfully direct the use of targeted therapy. Indeed, successful inhibition of BRAF or KRAS in metastatic CRCs driven by activating mutations in these genes requires combinations of drugs that inhibit the mutant protein while at the same time restraining adaptive resistance via CRC-specific EGFR-mediated feedback loops. The emerging paradigm is, therefore, that the intrinsic biology of CRC cells must be considered alongside the molecular profiles of individual tumours in order to successfully personalize treatment. In this Review, we outline how preclinical studies based on patient-derived models have informed the design of practice-changing clinical trials. The integration of these experiences into a common framework will reshape the future design of biology-informed clinical trials in this field.

A Critical Review of Second-Generation Anti-EGFR Monoclonal Antibodies in Metastatic Colorectal Cancer

BACKGROUND

Anti-EGFR monoclonal antibodies (mAbs) have become a relevant solution for the treatment of patients with metastatic colorectal cancer. Current anti-EGFR monoclonal antibodies face a series of problems, including resistance and non-durable response, and RAS and BRAF mutations serve as exclusion criteria for treatment with anti-EGFR mAbs. Advances in molecular tumor profiling and information on subsequent pathways responsible for disease progression and drug resistance helped develop a new generation of anti-EGFR mAbs. These second-generation mAbs have been developed to overcome existing resistance mechanisms and to limit common side effects. For the moment, existing literature suggests that these novel anti-EGFR mAbs are far from finding their way to clinical practice soon.

OBJECTIVE

In this review, we summarize and evaluate current data regarding ongoing research and completed clinical trials for different second-generation anti-EGFR monoclonal antibodies.

CONCLUSION

Anti-EGFR mAbs exhibit efficacy in advanced colorectal cancer, but second-generation mAbs failed to prove their benefit in the treatment of metastatic colorectal cancer. Understanding the biological basis of primary and acquired drug resistance could allow scientists to design better clinical trials and develop improved second-generation mAbs.

The Role of p53 Expression in Patients with RAS/BRAF Wild-Type Metastatic Colorectal Cancer Receiving Irinotecan and Cetuximab as Later Line Treatment

Background

Preclinical and clinical data indicate that p53 expression might modulate the activity of the epidermal growth factor receptor (EGFR), influencing response/resistance to anti-EGFR monoclonal antibodies. However, the association between p53 status and clinical outcome has not been clarified yet.

Objective

In our study, we evaluated the role of p53 expression in patients with RAS/BRAF wild-type metastatic colorectal cancer (mCRC) receiving irinotecan/cetuximab in an exploratory and a validation cohort.

Patients and Methods

p53 expression was analysed in patients with RAS/BRAF wild-type mCRC receiving second-line or third-line irinotecan/cetuximab. Survival distribution was assessed by the Kaplan–Meier method, while the log-rank test was used for survival comparison.

Results

Among 120 patients with RAS/BRAF wild-type mCRC included in our analysis, 52 (59%) and 19 (59%) patients showed p53 overexpression in the exploratory and validation cohort, respectively. In the exploratory cohort, low p53 expression was correlated with better median progression-free survival (hazard ratio 0.39; p < 0.0001), median overall survival (hazard ratio: 0.23; p < 0.0001) and response rate (p < 0.0001). These results were confirmed by data of the validation cohort where we observed better median progression-free survival (hazard ratio: 0.48; p = 0.0399), median overall survival (hazard ratio: 0.26; p = 0.0027) and response rate (p =0.0007) in patients with p53 normal expression mCRC.

Conclusions

In our study, p53 overexpression was associated with anti-EGFR treatment resistance in patients with RAS/BRAF WT mCRC, as confirmed in a validation cohort. Larger studies are needed to validate the role of p53 and investigate EGFR cross-talk in these patients.

Impact of EGFR and EGFR ligand expression on treatment response in patients with metastatic colorectal cancer

Up to 50% of patients with colorectal cancer (CRC) have either synchronous or metachronous hepatic metastases in the course of their disease. Patients with metastatic CRC (mCRC) whose tumors express wild-type KRAS benefit from treatment with monoclonal antibodies (such as cetuximab or panitumumab) that target the epidermal growth factor receptor (EGFR). However, the therapeutic response to these antibodies is variable, and further predictive models are required. The present study examined whether expression of different EGFRs or their ligands in tumors was associated with the response to cetuximab treatment. Tumor tissues, collected during liver resection in 28 patients with mCRC, were analyzed. The protein expression levels of EGFR/ErbB1, ErbB2, ErbB3 and the EGFR ligands heregulin and amphiregulin were determined using Luminex 200^® and enzyme-linked immunosorbent assays. Computed tomography or magnetic resonance imaging was performed 4 weeks before and 6-8 weeks after treatment with cetuximab. Response to treatment was assessed using the response evaluation criteria for solid tumors (RECIST). The association between the protein expression levels of different EGFRs and their ligands with RECIST criteria was then analyzed to determine whether these protein levels could predict the treatment response to cetuximab. A total of 12 patients exhibited a partial response, 9 exhibited stable disease and 7 exhibited progressive disease after cetuximab therapy according to RECIST. The expression levels of EGFRs (EGFR/ErbB1, ErbB2 and ErbB3) and their ligands (heregulin and amphiregulin) were not significantly associated with the response to cetuximab therapy. Therefore, the present study indicated that EGFR or EGFR ligand expression did not predict treatment response in patients with CRC with liver metastases following cetuximab therapy.

Anti-EGFR therapy in metastatic colorectal cancer: mechanisms and potential regimens of drug resistance

Cetuximab and panitumumab, as the highly effective antibodies targeting epidermal growth factor receptor (EGFR), have clinical activity in the patients with metastatic colorectal cancer (mCRC). These agents have good curative efficacy, but drug resistance also exists at the same time. The effects of KRAS, NRAS, and BRAF mutations and HER2 amplification on the treatment of refractory mCRC have been elucidated and the corresponding countermeasures have been put forward. However, the changes in EGFR and its ligands, the mutations or amplifications of PIK3CA, PTEN, TP53, MET, HER3, IRS2, FGFR1, and MAP2K1, the overexpression of insulin growth factor-1, the low expression of Bcl-2-interacting mediator of cell death, mismatch repair-deficient, and epigenetic instability may also lead to drug resistance in mCRC. Although the emergence of drug resistance has genetic or epigenetic heterogeneity, most of these molecular changes relating to it are focused on the key signaling pathways, such as the RAS/RAF/mitogen-activated protein kinase or phosphatidylinositol 3-kinase/Akt/mammalian target of the rapamycin pathway. Accordingly, numerous efforts to target these signaling pathways and develop the novel therapeutic regimens have been carried out. Herein, we have reviewed the underlying mechanisms of the resistance to anti-EGFR therapy and the possible implications in clinical practice.

Comprehensive review of targeted therapy for colorectal cancer

Colorectal cancer (CRC) is among the most lethal and prevalent malignancies in the world and was responsible for nearly 881,000 cancer-related deaths in 2018. Surgery and chemotherapy have long been the first choices for cancer patients. However, the prognosis of CRC has never been satisfying, especially for patients with metastatic lesions. Targeted therapy is a new optional approach that has successfully prolonged overall survival for CRC patients. Following successes with the anti-EGFR (epidermal growth factor receptor) agent cetuximab and the anti-angiogenesis agent bevacizumab, new agents blocking different critical pathways as well as immune checkpoints are emerging at an unprecedented rate. Guidelines worldwide are currently updating the recommended targeted drugs on the basis of the increasing number of high-quality clinical trials. This review provides an overview of existing CRC-targeted agents and their underlying mechanisms, as well as a discussion of their limitations and future trends.

Combined targeting of HER-2 and HER-3 represents a promising therapeutic strategy in colorectal cancer

Background

Abrogation of growth factor-dependent signaling represents an effective therapeutic strategy for patients with colorectal cancer (CRC). Here we evaluated the effectiveness of targeting the epidermal growth factor (EGF) receptors HER-2 and HER-3 in the three cell lines LS513, LS1034 and SW837.

Methods

Treatment with HER-2-specific antibodies trastuzumab and pertuzumab resulted in a mild reduction of cellular viability. In contrast, the antibody-drug conjugate T-DM1 mediated a strong and dose-dependent decrease of viability and Akt phosphorylation.

Results

The most striking effects were observed with the dual tyrosine kinase inhibitor lapatinib, and the Pan-ErbB inhibitor afatinib. Selectively, the effect of EGF receptor inhibition was augmented by a combination with 5-fluorouracil and oxaliplatin. Finally, high expression of HER-3 was detected in 121 of 172 locally advanced rectal cancers (70.3%). In conclusion, inhibition of EGF receptors effectively blocks downstream signaling and significantly impairs viability of CRC cells. However, the effectiveness of receptor inhibition highly depends on the inhibitors’ mode of action, as targeting HER-2 alone is not sufficient.

Conclusion

Since HER-2 and HER-3 are expressed in a relevant number of patients, targeting both receptors may represent a promising therapeutic strategy for CRC.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-6051-0) contains supplementary material, which is available to authorized users.

Association between the overexpression of Her3 and clinical pathology and prognosis of colorectal cancer: A meta-analysis

BACKGROUND

This study aimed to investigate the association between the overexpression of human epidermal growth factor receptor-3 (Her3) and the clinicopathological parameters and survival of patients with colorectal cancer (CRC).

METHODS

Relevant studies on the overexpression of Her3 (measured by immunohistochemistry) and overall survival (OS) in patients with CRC were searched for in PubMed, EMBASE, and Cochrane Library. Published data were extracted and computed into odds ratios (ORs) for assessing the association of Her3 overexpression with tumor differentiation, tumor node metastasis (TNM) stage, position of colon cancer, sex, and age. Prognostic data were computed into hazard ratios (HRs) for OS.

RESULTS

Eight studies including 1716 patients with CRC were included in this meta-analysis. The results revealed a significant association between Her3 overexpression and tumor differentiation [OR = 2.38; 95% confidence interval (95% CI): 1.76-3.22; P < .001], TNM tumor stage (OR = 0.71; 95% CI: 0.53-0.96; P = .03), and position of colon cancer (OR = 1.71; 95% CI: 1.28-2.27; P < .001). While patients with Her3 overexpression demonstrated a worse tumor response (OR = 0.31; 95% CI: 0.16-0.60; P < .001) and OS after treatment with cetuximab (HR = 1.86; 95% CI: 1.24-2.79; P = .003), they demonstrated better OS after symptomatic treatment (HR = 0.65; 95% CI: 0.50-0.85; P = .002). Her3 overexpression was not associated with sex (OR = 1.03; 95% CI: 0.83-1.28; P = .79), age (OR = 0.96; 95% CI: 0.75-1.24; P = .77), colon or rectum site (OR = 0.79; 95% CI: 0.44-1.43; P = .44), and total OS (HR = 1.09; 95% CI: 0.69-1.72; P = .72).

CONCLUSION

Her3 expression is associated with the clinical pathology and prognosis of CRC, which explains the nonefficacy of cetuximab treatment in patients with CRC.

Relationships between tumour response and primary tumour location, and predictors of long-term survival, in patients with RAS wild-type metastatic colorectal cancer receiving first-line panitumumab therapy: retrospective analyses of the PRIME and PEAK clinical trials

BACKGROUND

Data from two trials of panitumumab in metastatic colorectal cancer (mCRC) were retrospectively analysed to investigate the effects of primary tumour location on early-tumour shrinkage (ETS) and depth of response (DpR), and identify factors predicting long-term survival.

METHODS

Patients with RAS wild-type mCRC from PRIME (NCT00364013) and PEAK (NCT00819780) were included. ETS was defined as a ≥30% reduction in the sum-of-the-longest-diameters of measurable target lesions at eight weeks. DpR was the maximum percentage change from baseline to nadir in patients with shrinkage. Univariate and multivariate logistic analyses of short- versus long-term survivor data were performed.

RESULTS

A total of 435/559 (78%) patients had left-sided disease. Of these, a higher proportion of patients treated with panitumumab versus comparator achieved ETS (PRIME: 62% vs. 36%; PEAK: 58% vs. 41%); median DpR was also higher with panitumumab (PRIME: 59% vs. 49%; PEAK: 70% vs. 48%). In pooled analyses of the studies, more patients with right-sided disease achieved ETS if treated with panitumumab than comparator (39% vs. 29%). Panitumumab treatment consistently predicted long-term survival.

CONCLUSIONS

First-line panitumumab was associated with improved ETS and DpR vs. comparator in patients with left-sided mCRC. ETS may identify a subgroup of patients with right-sided disease who might respond to panitumumab.

Mechanisms of resistance to anti-EGFR therapy in colorectal cancer

Targeting the epidermal growth factor receptor (EGFR) either alone or in combination with chemotherapy is effective for patients with RAS wild type metastatic colorectal cancer (mCRC). However, only a small percentage of mCRC patients are sensitive to anti-EGFR therapy and even the best cases finally become refractory to this therapy. It has become apparent that the RAS mutations correlate with resistance to anti-EGFR therapy. However, these resistance mechanisms only account for nearly 35% to 50% of nonresponsive patients, suggesting that there might be additional mechanisms. In fact, several novel pathways leading to escape from anti-EGFR therapy have been reported in recent years. In this review, we provide an overview of known and novel mechanisms that contribute to both primary and acquired anti-EGFR therapy resistance, and enlist possible treatment strategies to overcome or reverse this resistance.

Comparative analysis of the EGFR, HER2, c-MYC, and MET variations in colorectal cancer determined by three different measures: gene copy number gain, amplification status and the 2013 ASCO/CAP guideline criterion for HER2 testing of breast cancer

Background

The purpose of this study was to explore gene copy number (GCN) variation of EGFR, HER2, c-MYC, and MET in patients with primary colorectal cancer (CRC).

Methods

Dual-colour silver-enhanced in situ hybridization was performed in tissue samples of 334 primary CRC patients. The amplification status (GCN ratio ≥2) and GCN gain (average GCN ≥4) data for the EGFR, HER2, c-MYC and MET genes were obtained. GCN variation was also assessed by the criterion of the 2013 ASCO/CAP guidelines for HER2 testing.

Results

Amplification of EGFR, HER2, c-MYC and MET was detected in 8 (2.4%), 20 (6.0%), 29 (8.7%), and 14 (4.2%) patients, respectively. Of 66 patients with at least one amplified gene, five exhibited co-amplification of genes studied (HER2-MET co-amplification: two patients; HER2-c-MYC co-amplification: two patients; EGFR-c-MYC co-amplification: one patient). There were 109 patients with GCN gains of one or more genes (EGFR: 11/334, HER2: 29/334, c-MYC; 60/334, MET: 48/334) and 32.1% (35/109) had multiple GCN gains. When each GCN was assessed by the criterion of the ASCO/CAP 2013 guideline for HER2 testing, 116 people showed positive or equivocal results for one or more genes. The cumulative amplification status had no association with patients’ outcome. However, the cumulative results of the GCN gain and GCN status determined according to the ASCO/CAP guideline had a significant prognostic correlation in the univariate analysis (P values of 0.006 and 0.022, respectively). In the multivariate analysis, GCN gain and GCN status were independent prognostic factors (P values of 0.010 and 0.017, respectively).

Conclusions

In this study, we evaluated GCN variation of four genes in a large sample of Korean CRC patients. The amplification status was not related to patient outcome. However, the GCN gain and GCN status according to the ASCO/CAP 2013 guideline were independent prognostic factors.

The role of primary tumour sidedness, EGFR gene copy number and EGFR promoter methylation in RAS/BRAF wild-type colorectal cancer patients receiving irinotecan/cetuximab

BACKGROUND

The data from randomised trials suggested that primary tumour sidedness could represent a prognostic and predictive factor in colorectal cancer (CRC) patients, particularly during treatment with anti-epidermal growth factor receptor (EGFR) therapy. However, an in-deep molecular selection might overcome the predictive role of primary tumour location in this setting.

METHODS

We conducted a retrospective analysis in which tumour samples from RAS/BRAF wild-type (WT) metastatic CRC patients treated with second-third-line irinotecan/cetuximab were analysed for EGFR gene copy number (GCN) and promoter methylation. Study objective was to evaluate the correlation of tumour sidedness, EGFR promoter methylation and EGFR GCN with clinical outcome. Median follow-up duration was 14.3 months.

RESULTS

Eighty-eight patients were included in the study, 27.3% had right-sided CRC, 72.7% had left-sided CRC; 36.4% had EGFR GCN<2.12 tumour, 63.6% had EGFR GCN⩾2.12 tumour; 50% had EGFR promoter-methylated tumour. Right-sided colorectal cancer (RSCRC) were associated with reduced overall response rate (ORR) (4.2% for RSCRC vs 35.9% for left sided colorectal cancer (LSCRC), P=0.0030), shorter progression-free survival (PFS) (3.0 vs 6.75 months, P<0.0001) and shorter overall survival (OS) (8 vs 13.6 months, P<0.0001). EGFR GCN<2.12 tumours were associated with reduced ORR (6.2% for EGFR GCN<2.12 vs 39.3% for EGFR GCN⩾2.12 tumours, P=0.0009), shorter PFS (3.5 vs 6.5 months, P=0.0006) and shorter OS (8.5 vs 14.0 months, P<0.0001). Epidermal growth factor receptor-methylated tumours were associated with reduced ORR (9.1% for methylated vs 45.5% for unmethylated, P=0.0001), shorter PFS (3 vs 7.67 months, P<0.0001) and shorter OS (8 vs 17 months, P<0.0001). At multivariate analysis, EGFR GCN and EGFR promoter methylation maintained their independent role for ORR (respectively P=0.0082 and 0.0025), PFS (respectively P=0.0048 and<0.0001) and OS (respectively P=0.0001 and<0.0001).

CONCLUSIONS

In our study, an accurate molecular selection based on an all RAS and BRAF analysis along with EGFR GCN and EGFR promoter methylation status seems to be more relevant than primary tumour sidedness in the prediction of clinical outcome during cetuximab/irinotecan therapy. However, these data need to be validated with future prospective and translational studies.

Prognostic significance of HER3 in patients with malignant solid tumors

Human epidermal growth factor receptor 3 (HER3) is closely involved in tumor progression and is an important target of therapy. To evaluate the prognostic significance of HER3 in malignant solid tumors, we searched the PUBMED, EMBASE and CNKI databases for relevant studies written in English or Chinese up to December 2015. Fifteen studies comprising 2964 patients were identified. The HER3⁺ rate ranged from 9.0-75.1 % in malignant solid tumors: 30.3-75.1 % in breast cancers, 51.1-74.5 % in colorectal cancers, 13.7-59.0 % in gastric cancers, and 54.5-74.4 % in cervical cancers. For patients with a malignant solid tumor, the death risk was higher for those with a HER3⁺ tumor than for those with a HER3⁻ tumor (HR 1.60, 95% CI: 1.27 - 2.02, P < 0.001). Subgroup analysis revealed this was also the case for patients with digestive or gastric cancer (HR 1.78, P < 0.001; HR 2.18, P < 0.001). By contrast, HER3 had no prognostic significance in colorectal or breast cancer (HR 1.52, P = 0.296; HR 1.23, P = 0.108). HER3⁺ is thus associated with poor survival in overall and in gastric cancer. The prognostic significance of HER3⁺ in other tumors is uncertain and deserves further study.

Methods of selecting combination therapy for colorectal cancer patients: a patent evaluation of US20160025730A1

INTRODUCTION

Colorectal cancer (CRC) is the fourth most common cancer worldwide. Targeted therapy drugs (TTDs) are a valid treatment, epithelial growth factor receptor (EGFR) inhibitors being one of the most commonly used for CRC patients. However, this treatment is only useful for patients with wild-type KRAS (wtKRAS) and is effective only on about 40 to 60% of this subset due to the high plasticity of ErbB network. Areas covered: The invention proposes the use of ErbB protein levels and ErbB receptor dimer formation as biomarkers for selecting, predicting and monitoring CRC patients showing sensitivity to the action of EGFR inhibitors to benefit from the combination therapy of EGFR and HER2 inhibitors. The in vitro data on Lim1215 cells suggest the over-activation of HER3 signaling pathway in response to the use of EGFR inhibitors on monotherapy; the use of HER2 or HER3 or MEK inhibitors in combination with EGFR inhibitors reversed this activation. Expert opinion: To assess the clinical applicability of this invention, further studies are needed since the conclusions are derived solely based on the data obtained from only one CRC cell line (Lim1215). Furthermore, other biofactors/mutations should be considered to assure the potential benefits of the combination therapies proposed.

Dual targeting of HER3 and EGFR in colorectal tumors might overcome anti-EGFR resistance

Multiple genetic alterations have been associated with resistance to anti-EGFR therapy in metastatic colorectal cancer (CRC) patients. Research has been mainly focused on driver mutations in KRAS, NRAS, BRAF and PI3K. However, recent evidence suggests a crucial role for non-genetic mechanisms in conferring resistance to anti-EGFR therapy. Specifically, the HER3 receptor is capable of heterodimerizing with multiple EGFR family members resulting in downstream activation of the PI3K and MAPK pathways. Monoclonal antibodies targeted against the HER3 receptor are being investigated in clinical trials; however, preliminary data has shown limited clinical activity. Thus, given the relevance of the HER3 receptor in activating downstream effector pathways and in conferring resistance to anti-EGFR therapy, the therapeutic targeting of HER3 in combination with primary drivers of the tumor is also being investigated. Here, we review the role of HER3 as a promoter of clinical resistance to EGFR therapy and discuss therapeutic approaches that could potentially overcome this resistance.

Biomarkers predicting resistance to epidermal growth factor receptor-targeted therapy in metastatic colorectal cancer with wild-type KRAS

EGFR pathway is an important therapeutic target in human tumors, including metastatic colorectal cancer (mCRC). The advent of EGFR-targeted monoclonal antibodies panitumumab and cetuximab has generated promise for the treatment of mCRC and has largely improved patients' progression-free survival (PFS) and overall survival (OS). However, treatment with anti-EGFR monoclonal antibodies is only effective in a subset of mCRC patients with wild-type KRAS. This indicates that there are other factors affecting the efficacy of anti-EGFR monoclonal antibodies. Existing studies have demonstrated that among colorectal cancer patients with wild-type KRAS, harboring mutations of BRAF, PIK3CA, NRAS, or PTEN-null may demonstrate resistance to anti-EGFR-targeted therapy, and biomarkers detection can provide better-personalized treatment for mCRC patients. How to identify and reverse the secondary resistance to anti-EGFR monoclonal antibody therapy is also another great challenge to improve the anti-EGFR efficacy in wild-type KRAS mCRC patients. Finally, both of the molecular mechanisms of response and acquired resistance would be important for the directions of future research. This review focuses on how to further improve the predictive value of anti-EGFR therapies and how to also try and avoid futile treatment for wild-type KRAS colorectal cancer patients.

A Randomized Phase II/III Study of Dalotuzumab in Combination With Cetuximab and Irinotecan in Chemorefractory, KRAS Wild-Type, Metastatic Colorectal Cancer

BACKGROUND

Insulin-like growth factor type 1 receptor (IGF-1R) mediates resistance to epidermal growth factor receptor (EGFR) inhibition and may represent a therapeutic target. We conducted a multicenter, randomized, double blind, phase II/III trial of dalotuzumab, an anti-IGF-1R monoclonal antibody, with standard therapy in chemo-refractory, KRAS wild-type metastatic colorectal cancer.

METHODS

Eligible patients were randomly assigned to dalotuzumab 10mg/kg weekly (arm A), dalotuzumab 7.5mg/kg every alternate week (arm B), or placebo (arm C) in combination with cetuximab and irinotecan. Primary endpoints were progression-free survival (PFS) and overall survival (OS). Secondary endpoints included exploratory biomarker analyses. All statistical tests were two-sided.

RESULTS

The trial was prematurely discontinued for futility after 344 eligible KRAS wild-type patients were included in the primary efficacy population (arm A = 116, arm B = 117, arm C = 111). Median PFS was 3.9 months in arm A (hazard ratio [HR] = 1.33, 95% confidence interval [CI] = 0.98 to 1.83, P = .07) and 5.4 months in arm B (HR = 1.13, 95% CI = 0.83 to 1.55, P = .44) compared with 5.6 months in arm C. Median OS was 10.8 months in arm A (HR = 1.41, 95% CI = 0.99 to 2.00, P = .06) and 11.6 months in arm B (HR = 1.26, 95% CI = 0.89 to 1.79, P = .18) compared with 14.0 months in arm C. Grade 3 or higher asthenia and hyperglycaemia occurred more frequently with dalotuzumab compared with placebo. In exploratory biomarker analyses, patients with high IGF-1 mRNA tumors in arm A had numerically better PFS (5.6 vs 3.6 months, HR = 0.59, 95% CI = 0.28 to 1.23, P = .16) and OS (17.9 vs 9.4 months, HR = 0.67, 95% CI = 0.31 to 1.45, P = .31) compared with those with high IGF-1 mRNA tumors in arm C. In contrast, in arm C high IGF-1 mRNA expression predicted lower response rate (17.6% vs 37.3%, P = .04), shorter PFS (3.6 vs 6.6 months, HR = 2.15, 95% CI = 1.15 to 4.02, P = .02), and shorter OS (9.4 vs 15.5 months, HR = 2.42, 95% CI = 1.21 to 4.82, P = .01).

CONCLUSIONS

Adding dalotuzumab to irinotecan and cetuximab was feasible but did not improve survival outcome. IGF-1R ligands are promising biomarkers for differential response to anti-EGFR and anti-IGF-1R therapies.

Prospective study of a molecular selection profile for RAS wild type colorectal cancer patients receiving irinotecan-cetuximab

Background

The aim of our study was to evaluate whether a panel of biomarkers, prospectively analysed might be able to predict patients’ clinical outcome more accurately than RAS status alone.

Methods

K-RAS (exons 2, 3, 4) wild type colorectal cancer patients, candidates to second/third-line cetuximab with chemotherapy were prospectively allocated into 2 groups on the basis of their profile: favourable (BRAF and PIK3CA exon 20 wild type, EGFR GCN ≥ 2.6, HER-3 Rajkumar score ≤ 8, IGF-1 immunostaining < 2) or unfavourable (any of the previous markers altered or mutated). After the introduction of N-RAS status (exons 2, 3, 4) only RAS wild type patients were considered eligible.

Primary aim was response rate (RR). To detect a difference in terms of RR among patients with an unfavourable profile (estimated around 25%) and patients with a favourable profile (estimated around 60%), with a probability alpha of 0.05 and beta of 0.05, required sample size was 46 patients. Secondary endpoints were progression free survival (PFS) and overall survival (OS).

Results

Forty-six patients were enrolled. Seventeen patients (37%) were allocated to the favourable and 29 patients (63%) to the unfavourable profile. RR in the favourable and unfavourable group was 11/17 (65%) and 2/29 (7%) (p = 0.007) respectively. The favourable group also showed an improved PFS (8 months vs. 3 months, p < 0.0001) and OS (15 months vs. 6 months, p < 0.0001).

Conclusions

Our results suggest that prospective selection of optimal candidates for cetuximab treatment is feasible and may be able to improve clinical outcome.

Gene expression markers of efficacy and resistance to cetuximab treatment in metastatic colorectal cancer: results from CALGB 80203 (Alliance)

PURPOSE

Formalin-fixed, paraffin-embedded tumor samples from CALGB 80203 were analyzed for expression of EGFR axis-related genes to identify prognostic or predictive biomarkers for cetuximab treatment.

PATIENTS AND METHODS

Patients (238 total) with first-line metastatic colorectal cancer (mCRC) were randomized to FOLFOX or FOLFIRI chemotherapy ± cetuximab. qRT-PCR analyses were conducted on tissues from 103 patients at baseline to measure gene expression levels of HER-related genes, including amphiregulin (AREG), betacellulin (BTC), NT5E (CD73), DUSP4, EGF, EGFR, epigen (EPGN), epiregulin (EREG), HBEGF, ERBB2 (HER2), ERBB3 (HER3), ERBB4 (HER4), PHLDA1, and TGFA. The interactions between expression levels and treatment with respect to progression-free survival (PFS) and overall survival (OS) were modeled using multiplicative Cox proportional hazards models.

RESULTS

High tumor mRNA levels of HER2 [hazard ratio (HR), 0.64; P = 0.002] and EREG (HR, 0.89; P = 0.016) were prognostic markers associated with longer PFS across all patients. HER3 and CD73 expression levels were identified as potential predictive markers of benefit from cetuximab. In KRAS wild-type (WT) tumors, low HER3 expression was associated with longer OS from cetuximab treatment, whereas high HER3 expression was associated with shorter OS from cetuximab treatment (chemo + cetuximab: HR, 1.15; chemo-only: HR, 0.48; Pinteraction = 0.029). High CD73 expression was associated with longer PFS from cetuximab treatment in patients with KRAS-WT (chemo + cetuximab: HR, 0.91; chemo-only: HR, 1.57; Pinteraction = 0.026) and KRAS-mutant (Mut) tumors (chemo + cetuximab: HR, 0.80; chemo-only: HR, 1.29; P = 0.025).

CONCLUSIONS

Gene expression of HER3 and CD73 was identified as a potential predictive marker for cetuximab. These data implicate HER axis signaling and immune modulation as potential mechanisms of cetuximab action and sensitivity.

Beyond KRAS status and response to anti-EGFR therapy in metastatic colorectal cancer

In patients with metastatic colorectal cancer, overall survival has improved over the last decade mainly due to the use of effective targeted therapies such as anti-EGFR. However, survival improvement is linked to proper selection of patients expected to benefit from these treatments. KRAS codons 12 and 13 mutation status was the first validated molecular biomarker for anti-EGFR antibodies. Today, rare KRAS alterations and NRAS mutations were implemented, defining the 'RAS' status as the new validated marker of response to anti-EGFR antibodies. Moreover, other biomarkers are under investigation to screen for other targets and help with patients selection. Here, we reviewed these promising biomarkers: mutations in the RAS-MAPK and PI3K-AKT pathways genes, MET activation, HER/ErbB receptors activation (EGFR, HER2 and HER3), EGFR ligands, antibody-dependent cell-mediated cytotoxicity) and miRNAs. Further data are needed to define their impact for the treatment of patients with metastatic colorectal cancer.

Pyrosequencing evaluation of low-frequency KRAS mutant alleles for EGF receptor therapy selection in metastatic colorectal carcinoma

AIM

To evaluate whether pyrosequencing (PS) improves the KRAS mutational status predictive value.

PATIENTS & METHODS

A retrospective analysis of KRAS mutations by PS and direct sequencing (DS) in 192 metastatic colorectal carcinomas (mCRCs), subgrouped in 51 KRAS mutated at PS and 141 KRAS wild-type at DS.

RESULTS

DS failed to detect low-frequency KRAS mutations in four out of 51 mCRCs, whereas PS detected 12 additional low-frequency KRAS mutations in 141 mCRCs KRAS wild-type at DS. After reanalyzing by PS 97 KRAS wild-type tumors treated with anti-EGF receptor (EGFR) antibodies, nine additional mutations were revealed in nonresponders, whereas none of responders exhibited a KRAS-mutated genotype. Of note, KRAS-mutated tumors upon PS showed a worst progression-free survival after EGFR therapy. Finally, PS allowed the detection of additional NRAS, BRAF and exon 20 PIK3CA mutations mostly in KRAS wild-type mCRCs resistant to EGFR therapy.

CONCLUSION

PS detection of low-frequency mutations may improve the KRAS predictive value for EGFR therapy selection.

EGFR gene copy number as a predictive biomarker for resistance to anti-EGFR monoclonal antibodies in metastatic colorectal cancer treatment: a meta-analysis

OBJECTIVE

The epidermal growth factor receptor (EGFR) inhibitors monoclonal antibodies (MoAbs) have already shown the therapeutic effectiveness in patients with metastatic colorectal cancer (mCRC). But many patients resist to the treatment. The aim of this meta-analysis was to assess EGFR gene copy number (GCN) as a candidate predictive biomarker for resistance to anti-EGFR MoAbs in mCRC treatment.

METHODS

Systematic computerized searches of the PubMed, EMBase and Cochrane Library were performed. The primary endpoint was objective response rate (ORR). The second endpoints included progression-free survival (PFS), and overall survival (OS). The pooled odd ratio (OR) and pooled sensitivity, specificity, and summary receiver operator characteristic (SROC) for ORR were estimated. The pooled hazard ratios (HR) for PFS and OS were also calculated.

RESULTS

Fourteen studies with 1,021 patients were included. Increased EGFR GCN was associated with increased ORR (OR=6.905; 95% CI: 4.489-10.620). It was also found in wild-type KRAS mCRC patients, with the pooled OR of 8.133 (95% CI: 4.316-15.326). GCN has medium value for predicting ORR, with the pooled sensitivity of 0.79 (95% CI: 0.73-0.84), the pooled specificity of 0.59 (95% CI: 0.55-0.62). In wild-type KRAS mCRC patients, the sensitivity and the specificity were 0.80 (95% CI: 0.70-0.87) and 0.60 (95% CI: 0.53-0.66), respectively. Increased EGFR GCN was associated with increased PFS (HR=0.557; 95% CI: 0.382-0.732) and OS (HR=0.579; 95% CI: 0.422-0.737).

CONCLUSIONS

This meta-analysis suggests that EGFR GCN represents a predictive biomarker for tumor response in mCRC patients treated with MoAbs regardless of KRAS mutation. mCRC patients with increased EGFR GCN are more likely to have a better response, PFS, and OS when treated with cetuximab or panitumumab.

The prognostic role of ephrin A2 and endothelial growth factor receptor pathway mediators in patients with advanced colorectal cancer treated with cetuximab

BACKGROUND

Patients with colorectal cancer (CRC) with wild-type KRAS mutations are often treated with the endothelial growth factor receptor (EGFR) monoclonal antibody cetuximab. Despite the presence of a specific molecular target, most patients still do not derive benefit from this biological treatment. Our study explores the role of ephrin A2 (EphA2) receptor expression and of EGFR pathway mediators as predictors of cetuximab benefit.

PATIENTS AND METHODS

Formalin-fixed paraffin-embedded (FFPE) tumor biopsy samples from 226 cetuximab-treated patients with CRC were studied for mRNA expression of insulin growth factor binding protein 2 (IGFBP2), insulin growth factor receptor 1 (IGF1R), cMET, EphA2, human epidermal growth factor receptor 2 (HER2), HER3, and HER4 by means of TaqMan reverse-transcribed polymerase chain reaction (RT-PCR).

RESULTS

Of the 226 patients evaluable for exploratory analysis, 222 had complete data from follow-up visits. The univariate analysis revealed the following significant adverse prognostic factors for risk of death: high EphA2 mRNA levels (hazard ratio [HR], 1.61; P = .015), high HER2 mRNA levels (HR, 1.51; P = .045), and high IGF1R mRNA levels (HR, 1.56; P = .021). Low EphA2 tumor expression was significantly associated with objective response to cetuximab therapy. In multivariate analysis of a broad biomarker panel, factors with independent prognostic value included EphA2 mRNA levels (HR, 1.67; P = .029), high amphiregulin (AREG) mRNA levels in KRAS wild-type tumors (HR, 0.17; P < .0001), and high epiregulin (EREG) mRNA levels (HR, 0.38; P = .006).

CONCLUSION

High EphA2 receptor expression in CRC was associated with a worse outcome in patients treated with cetuximab-based therapy. Prospective validation in treated and control patients is required to dissect the predictive from prognostic role in advanced CRC.

Role of β4 integrin in HER-3-negative, K-RAS wild-type metastatic colorectal tumors receiving cetuximab

AIMS

Altered α6β4 integrin expression has been demonstrated in HER-3-negative tumors and may be responsible for anti-HER treatment resistance. The current study aimed to evaluate the interaction between polymorphisms of α6 and β4 integrins and clinical outcome in HER-3-negative, K-RAS wild-type colorectal cancer patients receiving cetuximab.

PATIENTS & METHODS

K-RAS analysis was performed via direct sequencing, HER-3 was evaluated by immunohistochemistry and genotyping of α6 and β4 integrins was performed by real-time PCR.

RESULTS

An univariate analysis, the β4 rs8669, rs871443 and rs9367 polymorphisms correlated with progression-free and overall survival. On multivariate analysis, only the β4 rs8669 maintained an independent role in influencing progression-free survival.

CONCLUSION

We believe that β4 rs8669 genotyping may help to identify a subgroup of HER-3-negative, K-RAS wild-type colorectal cancer patients who are more likely to benefit from anti-EGFR treatment. Our findings could also be relevant in planning future trials testing treatment strategies against the integrin-activated molecular pathways.

Targeting mechanisms of resistance to anti-EGF receptor therapy in KRAS wild-type colorectal cancer: the path to more personalized medicine

The targeting of EGF receptors (EGFRs) in metastatic colorectal cancer has improved the outcome of patients with KRAS wild-type tumors. However, these improvements have been modest and do not translate across all patients with KRAS wild-type tumors. Better understanding of the EGFR pathway has led to the exploration of variable novel potential biomarkers of resistance and response to anti-EGFR therapy. This manuscript will focus on recently identified mechanisms of resistance to anti-EGFR therapy in KRAS wild-type colorectal cancer. Subsequently, an assessment will be presented on how the current understanding of some of these mechanisms of resistance has led, and will lead, to novel therapeutic opportunities in the management of colorectal cancer.

EGFR gene copy number as a prognostic marker in colorectal cancer patients treated with cetuximab or panitumumab: a systematic review and meta analysis

Background

The epidermal growth factor receptor (EGFR) gene copy number (GCN) has been previously demonstrated to correlate with the clinical outcome of colorectal cancer (CRC) treated with anti-EGFR monoclonal antibodies (mAbs), although it remains controversial. We conducted a systematic review and meta-analysis to assess EGFR GCN as a potential biomarker of survival for patients with advanced CRC receiving treatment with anti-EGFR mAbs.

Methods

We systematically identified articles investigating EGFR GCN by fluorescent or chromogenic in situ hybridization or other detection techniques in patients with metastatic CRC treated with panitumumab or cetuximab, (last search: 10 August 2012). Eligible studies had to report on overall survival (OS), progression-free survival (PFS) or time-toprogression (TTP), stratified by EGFR GCN. Summary hazard ratios (HRs) were calculated using random-effects models.

Results

Among 13 identified studies, 10 (776 patients, 302 with increased GCN), 8 (893 patients, 282 with increased GCN) and 3 (149 patients, 66 with increased GCN) were eligible for the OS, PFS and TTP meta-analyses, respectively. Increased EGFR GCN was associated with increased OS (HR = 0.62; 95% CI 0.50–0.77; P<0.001), PFS (HR = 0.65; 95% CI 0.47–0.89; P = 0.008) but not TTP (HR = 0.71; 95% CI 0.44–1.14; P = 0.157). It was also shown that EGFR GCN is independent of other factors such as KRAS status. Among those populations received second-line or higher treatment, increased EGFR GCN was strongly associated with improved survival (for OS, HR = 0.60; 95% CI 0.47–0.75; P<0.001; for PFS, HR = 0.59; 95% CI 0.47–0.75; P<0.001), whereas it did not influence survival in patients that received first-line therapy.

Conclusion

Among the anti-EGFR-treated patients, increased EGFR GCN appears to be associated with improved survival outcomes. The effect on survival appears to be related to patients receiving the line of treatment.

Mechanisms of acquired resistance to anti-EGF receptor treatment in colorectal cancer

SUMMARY The anti-EGFR monoclonal antibodies, cetuximab and panitumumab, are effective in a subset of colorectal cancer patients. However, acquisition of resistance to these drugs invariably develops. Elucidation of the molecular mechanisms underlying resistance is a crucial first step to develop therapeutic strategies to bypass secondary resistance. Three mechanisms of resistance have been characterized in patients so far: a mutation in the extracellular domain of EGFR preventing cetuximab-EGFR binding – interestingly, this mutation does not affect panitumumab effectiveness; activation of EGFR-related receptor HER2 by amplification or ligand overexpression; emergence of KRAS mutations or amplification. Importantly, already approved drugs can be used to bypass known mechanisms of resistance. Large-scale studies including biopsy at progression and prospective clinical trials are warranted.