Mechanisms of resistance to EGFR inhibitors in colorectal cancers

SUMMARY 

The EGF receptor (EGFR) is important in the regulation of proliferation, apoptosis and angiogenesis in cancer. EGFR inhibitors have become a mainstay of treatment of metastatic colorectal cancer, in particular KRAS wild-type patients in 50–60% of patients. Despite this many patients do not respond to these agents. Over the last few years the molecular basis of resistance to EGFR inhibitors has been elucidated to a certain degree. Mutations in KRAS and the NRAS exon are unlikely to respond to EGFR inhibitors. Other mutations, such as BRAF, PI3KCA/AKT and MET, may also lead to resistance. A greater understanding of the molecular basis for resistance may lead to ways of overcoming this, leading to improvements in care for patients.

Changing monoclonal antibody keeping unaltered the chemotherapy regimen in metastatic colorectal cancer patients: is efficacy maintained?

Monoclonal antibodies bevacizumab and cetuximab both improve overall survival (OS), progression free survival (PFS) and overall response rate (ORR) when combined with irinotecan-containing regimens. The optimal sequence of these monoclonal antibodies in combination with chemotherapy is controversial. This study analysed the efficacy of cetuximab plus Folfiri after progression with the same regimen plus bevacizumab in patients with metastatic colorectal cancer (mCRC). Patients are eligible if progressive disease (PD) after Folfiri-bevacizumab; ECOG PS 0–1. Primary endpoint is the disease control rate (DCR:ORR plus stable disease > 6 months); secondary endpoints: ORR, PFS, duration of response, OS and toxicity. ORR and DCR were reported with their confidence interval at 95%. Kaplan-Meier method was used for PFS and OS evaluation. Results: 54 patients were enrolled to receive Folfiri-cetuximab after PD to Folfiri-bevacizumab treatment. Median age was 65 (43–80), M/F 31/23, ECOG PS 0/1 was 36/ 18, WT Kras 33(61%). The DCR was 64.8% (CI 95% 52.1-77.5). Among the group of patients with stable or progressive disease at first line treatment, 13.3% of them obtained a response at second line. For second line treatment median duration of response was 6 months and clinical benefit 7 months. The ORR was 22.2% (CI 95% 11.1-33.3). The median progression-free survival was 7 months (CI 95% 6–8). The median overall survival for second line treatment was 14 months (CI 95% 11–17). No grade 4 toxicity was observed. Data suggest that this sequential combination therapy is active and well tolerated. At disease progression to first line chemotherapy treatment the maintenance of the same chemotherapy regimen and the change of the monoclonal antibody showed efficacy in response and survival in patients with mCRC.

Molecular detection of epidermal growth factor receptor in colorectal cancer: does it still make sense?

AIM

The aim of the study was to detect and compare the epidermal growth factor receptor (EGFr) content using different methods, to establish whether the quantitative detection and functional study of EGFr in colorectal cancer, using methods other than immunohistochemistry (IHC), are appropriate.

METHOD

Analysis of EGFr by IHC was performed in 230 colorectal cancer patients using monoclonal anti-EGFr. Total and activated EGFr (pY1068) contents were determined in 92 patients and real-time PCR, to determine the level of EGFr messenger RNA, was carried out in 60 patients.

RESULTS

There was no association between EGFr IHC groups and the mean total EGFr levels measured using ELISA.

CONCLUSION

The study shows that the results of different EGFr detection methods do not correlate with each other. Hence, the real role of EGFr in colorectal cancer remains unsettled. Clinically, the receptor itself does not seem to be important and it would be better to focus on EGFr signalling in downstream pathways.

Progress in metastatic colorectal cancer: growing role of cetuximab to optimize clinical outcome

The prognosis of metastatic colorectal cancer remains poor despite advances made in recent years, particularly with new treatments directed towards molecular targets. Cetuximab, a chimeric immunoglobulin (Ig)G1 monoclonal antibody that targets the ligand-binding domain of the epidermal growth factor receptor (EGFR), is active in metastatic colorectal cancer. As an IgG1 antibody, cetuximab may exert its antitumour efficacy through both EGFR antagonism and antibody-dependent cell-mediated cytotoxicity. The benefits of cetuximab in metastatic colorectal cancer are well documented in clinical trials and are acknowledged in the approval and licensing of this agent. There is evidence of the role of cetuximab not only in irinotecan-refractory or heavily pretreated patients, but also of the efficacy and safety of the addition of this agent to FOLFIRI (irinotecan/5-fluorouracil/leucovorin) in first-line metastatic colorectal cancer, with an enhanced effect in 5-fluorouracil patients with Kirsten rat sarcoma (KRAS) wild-type tumours. In these patients, a recent meta-analysis of the pooled Cetuximab Combined with Irinotecan in First-Line Therapy for Metastatic Colorectal Cancer (CRYSTAL) and Oxaliplatin and Cetuximab in First-Line Treatment of mCRC (OPUS) patient populations confirms that the addition of cetuximab to first-line chemotherapy achieves a statistically significant improvement in the best overall response, overall survival time, and progression-free survival (PSF) compared with chemotherapy alone. In nonresectable colorectal liver metastases, cetuximab plus FOLFOX-6 (oxaliplatin/5-fluorouracil/leucovorin) or cetuximab plus FOLFIRI increased significantly resectability of liver metastases, including R0 resections. Also, preliminary data indicate that cetuximab can be administered in a more convenient 2-week schedule in combination with standard chemotherapy. Cetuximab is generally well tolerated. Acne-form rash is the most frequent toxicity. Up to the present time, the results obtained with targeted therapy combinations are not as encouraging as initially expected. The identification of biomarkers associated with disease control, including KRAS and BRAF mutation status in patients treated with cetuximab, is changing the current management of metastatic colorectal cancer. Clinical and molecular predictive markers of response are under active evaluation in order to better select patients who could benefit from cetuximab treatment, with the aim of both optimising patient outcomes and avoiding unnecessary toxicities.

KRAS mutational status as a predictor of epidermal growth factor receptor inhibitor efficacy in colorectal cancer

Inhibitors of the epidermal growth factor receptor (EGFR) have demonstrated promising potential in the treatment of advanced colorectal cancer. However, a proportion of patients do not respond to therapy with EGFR inhibitors, and therefore, there has been interest in identifying those patients most likely to benefit from therapy with these agents. KRAS, a member of the RAS family of signaling proteins, plays an important role in EGFR-mediated regulation of cellular proliferation and survival. Although there is still some debate regarding the prognostic importance of KRAS mutations in patients with metastatic colorectal cancer, several recent phase 2 and 3 studies have identified the presence of mutations at codons 12 and 13 of KRAS as predictors of poor response to the anti-EGFR monoclonal antibodies panitumumab and cetuximab. Patients with wild-type KRAS were found to have significantly better progression-free survival, overall survival, and/or objective response rate compared with patients harboring KRAS mutations. As a result, there has been growing interest in the development of KRAS mutational status as a biomarker for predicting patient response to EGFR-targeted therapy. Screening colorectal tumors for the absence of KRAS mutations may help identify patients most likely to benefit from anti-EGFR therapies.

KRAS mutation testing in human cancers: The pathologist's role in the era of personalized medicine

A number of studies have shown that although antiepidermal growth factor receptor (EGFR) monoclonal antibodies are effective treatments for metastatic colorectal cancer (mCRC), only patients with wild-type KRAS tumors derive clinical benefit from these therapies. The anti-EGFR monoclonal antibodies panitumumab and cetuximab are approved in the United States for treatment of mCRC refractory to chemotherapy but are not recommended for use in patients with mutations in KRAS codons 12 or 13. Similarly, panitumumab is approved for the treatment of mCRC only in patients with wild-type KRAS in Europe and Canada. It is clear that KRAS mutational analysis will become an important aspect of disease management in patients with mCRC. Consequently, it will be important for pathologists and oncologists to develop and agree on standardized KRAS testing and reporting procedures to ensure optimum patient care. Pathologists will be central to this process because of their crucial role in selecting appropriate tumor specimens for testing, choosing the molecular diagnostic laboratory to be used, assisting in the selection of a suitable KRAS test, and interpreting the results of KRAS mutational analysis. Guidelines for KRAS testing that address these and other important points of consideration have recently been proposed in the United States and the European Union.

Vascular Endothelial Growth Factor plus Epidermal Growth Factor Receptor Dual Targeted Therapy in Metastatic Colorectal Cancer: Synergy or Antagonism?

There has been an intensive effort to develop novel therapies for the treatment of metastatic colorectal cancer (mCRC). The anti-epidermal growth factor receptor (EGFR) antibodies panitumumab and cetuximab and the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab have demonstrated clinical efficacy and acceptable toxicity in the treatment of mCRC as single agents or in combination with chemotherapy. Recent clinical trials have explored the efficacy and safety of treatment regimens incorporating chemotherapy in combination with bevacizumab and either panitumumab or cetuximab in patients with mCRC. Results from the BOND-2 trial, which investigated cetuximab, bevacizumab, and chemotherapy in mCRC, provided support for this therapeutic approach. Two large randomized phase 3 trials were initiated to evaluate firstline treatment of mCRC. The Panitumumab Advanced Colorectal Cancer Evaluation (PACCE) study investigated the efficacy and safety of oxaliplatin- or irinotecan-based chemotherapy and bevacizumab with or without panitumumab; CAIRO2 assessed the efficacy and safety of capecitabine/oxaliplatin and bevacizumab with or without cetuximab. In both trials, the combination of bevacizumab, an EGFR-specific antibody, and chemotherapy in first-line treatment of mCRC was associated with increased toxicity and no improvement in patient outcome. These results suggest that these specific combinations should not be used in first-line mCRC outside investigational studies.

Anti-epidermal growth factor receptor monoclonal antibodies in cancer therapy

The epidermal growth factor receptor (EGFR) is a transmembrane tyrosine kinase receptor involved in the proliferation and survival of cancer cells. EGFR is the first molecular target against which monoclonal antibodies (mAb) have been developed for cancer therapy. Here we review the mechanisms underlying the effects of EGFR-specific mAb in cancer therapy. The efficacy of EGFR-specific mAb in cancer occurs thanks to inhibition of EGFR-generated signalling; furthermore, the effects of antibodies on the immune system seem to play an important role in determining the overall anti-tumour response. In this review, attention is focused on cetuximab and panitumumab, two mAb introduced recently into clinical practice for treatment of metastatic colorectal and head and neck cancer which target the external part of EGFR.

Future directions in neoadjuvant therapy of rectal cancer: maximizing pathological complete response rates

Neoadjuvant therapy is widely accepted as the current standard of care for localized rectal cancer. Downstaging of disease has been significantly improved and pathological complete response rates (pCR) which were historically below 10% with preoperative radiation alone, now range from 15% to 30% with preoperative chemo-radiation. While the availability of new chemotherapeutic drugs (Irinotecan, Oxaliplatin, etc.) and molecular targeted agents (Bevacizamab, Cetuximab, etc.) hold a great deal of promise, results of recent studies indicate that the pCR rate with neoadjuvant therapy appears to have plateaued at 20-30%. The use of more intensive multidrug combinations has, however, significantly increased the toxicity of treatment. New paradigms in neoadjuvant therapy are therefore needed to further improve results of treatment. This review presents strategies for neoadjuvant therapy, with the potential to improve pCR rates and also survival of patients.

Chemotherapy with targeted agents for the treatment of metastatic colorectal cancer

The introduction of novel agents targeted to specific molecular features of cancer cells promises more options and marked improvements in efficacy for treatment of colon cancer. This overview of clinical studies describes the effects of administering the targeted agents bevacizumab, cetuximab, and panitumumab, also known as monoclonal antibodies, to treat metastatic colorectal cancer (mCRC) patients. All three targeted agents have been approved for use by the U.S. Food and Drug Administration and the European Agency for the Evaluation of Medicinal Products. Bevacizumab has been shown to extend survival when used in combination with irinotecan and 5-fluorouracil-based chemotherapy, and the addition of cetuximab to irinotecan and 5-fluorouracil-based chemotherapy overcomes irinotecan resistance. Cetuximab and panitumumab are both efficacious among refractory mCRC patients with wild-type KRAS tumors. Other targeted agents, for example, the tyrosine kinase inhibitors erlotinib, gefitinib, sunitinib, and vatalanib (PTK787/ZK 222584), are currently in various stages of clinical development.

Individualized therapies in colorectal cancer: KRAS as a marker for response to EGFR-targeted therapy

Individualized therapies that are tailored to a patient's genetic composition will be of tremendous value for treatment of cancer. Recently, Kirsten ras (KRAS) status has emerged as a predictor of response to epidermal growth factor receptor (EGFR) targeted therapies. In this article, we will discuss targeted therapies for colorectal cancers (CRC) based on EGFR signaling pathway and review published data about the potential usefulness of KRAS as a biological marker for response to these therapies. Results from relevant studies published since 2005 and unpublished results presented at national meetings were retrieved and summarized. These studies reflected response (or lack of response) to EGFR-targeted therapies in patients with metastatic CRC as a function of KRAS status. It has become clear that patients with colorectal cancer whose tumor has an activating mutation in KRAS do not respond to monoclonal antibody therapies targeting EGFR. It should now become a standard practice that any patients being considered for EGFR targeted therapies have their tumors tested for KRAS status and only those with wild-type KRAS being offered such therapies.

Cetuximab and chemotherapy as initial treatment for metastatic colorectal cancer

BACKGROUND

We investigated the efficacy of cetuximab plus irinotecan, fluorouracil, and leucovorin (FOLFIRI) as first-line treatment for metastatic colorectal cancer and sought associations between the mutation status of the KRAS gene in tumors and clinical response to cetuximab.

METHODS

We randomly assigned patients with epidermal growth factor receptor-positive colorectal cancer with unresectable metastases to receive FOLFIRI either alone or in combination with cetuximab. The primary end point was progression-free survival.

RESULTS

A total of 599 patients received cetuximab plus FOLFIRI, and 599 received FOLFIRI alone. The hazard ratio for progression-free survival in the cetuximab-FOLFIRI group as compared with the FOLFIRI group was 0.85 (95% confidence interval [CI], 0.72 to 0.99; P=0.048). There was no significant difference in the overall survival between the two treatment groups (hazard ratio, 0.93; 95% CI, 0.81 to 1.07; P=0.31). There was a significant interaction between treatment group and KRAS mutation status for tumor response (P=0.03) but not for progression-free survival (P=0.07) or overall survival (P=0.44). The hazard ratio for progression-free survival among patients with wild-type-KRAS tumors was 0.68 (95% CI, 0.50 to 0.94), in favor of the cetuximab-FOLFIRI group. The following grade 3 or 4 adverse events were more frequent with cetuximab plus FOLFIRI than with FOLFIRI alone: skin reactions (which were grade 3 only) (in 19.7% vs. 0.2% of patients, P<0.001), infusion-related reactions (in 2.5% vs. 0%, P<0.001), and diarrhea (in 15.7% vs. 10.5%, P=0.008).

CONCLUSIONS

First-line treatment with cetuximab plus FOLFIRI, as compared with FOLFIRI alone, reduced the risk of progression of metastatic colorectal cancer. The benefit of cetuximab was limited to patients with KRAS wild-type tumors. (ClinicalTrials.gov number, NCT00154102.)

Anti-epidermal growth factor receptor monotherapy in the treatment of metastatic colorectal cancer: where are we today?

Over the past 10 years there has been a significant increase in the armamentarium of agents available for use in the treatment of advanced colorectal cancer (CRC). Among these new agents are two monoclonal antibodies targeting the epidermal growth factor receptor (EGFR): cetuximab, a mouse-human chimeric monoclonal antibody, and panitumumab, a fully human monoclonal antibody. Both are approved as monotherapy for the treatment of chemotherapy-refractory advanced CRC. Cetuximab is also indicated for use in combination with irinotecan. Here, we review 10 reports of phase II and III clinical studies of patients treated with panitumumab or cetuximab monotherapy. The clinical trials demonstrate similar efficacy profiles for advanced CRC patients treated with panitumumab and cetuximab monotherapy, with some differences in their adverse event profiles. In addition, the recent results of retrospective tumor KRAS gene mutational analyses in CRC patients treated with anti-EGFR monotherapy are reviewed. Data from the clinical trials reviewed here clearly demonstrate that anti-EGFR monotherapy is an effective treatment modality for patients with chemotherapy-refractory advanced CRC.

Experimental results and related clinical implications of PET detection of epidermal growth factor receptor (EGFr) in cancer

The epidermal growth factor receptor (EGFr) is one of the most studied molecules as a target for cancer therapy. Over these last few years, several studies attempting to identify predictive biomarkers of treatment response, such as the receptor status or other molecules related to the downstream signalling pathway, have been conducted. However, from a clinical point of view, the information obtained from ex vivo analyses still has various limitations that may be overcome by the combination with molecular imaging technologies which may provide a noninvasive, global, in vivo evaluation of the molecular tumour background. The aim of this review is to report the preclinical results of all positron emission tomography (PET) tracers synthesized until now for in vivo detection of EGFr in cancer. Two classes of PET compounds have been developed: labelled small molecules such as tyrosine kinase inhibitors and labelled monoclonal antibodies. The in vitro and in vivo results of these PET tracers are very different depending on the chemical properties, positron emission radionuclide, or animal models. As a consequence, various critical questions are still open, and the implications of a translation in the clinical setting for EGFr imaging in cancer patients is discussed.