Cetuximab rechallenge in metastatic colorectal cancer patients: how to come away from acquired resistance?

Targeted therapy for metastatic colorectal cancer

INTRODUCTION

Outcomes in metastatic colorectal cancer are improving, with better understanding and use of targeted therapies. Areas covered: A review of the literature and recent conference presentations was undertaken on the topic of systemic treatment of metastatic colorectal cancer. This article reviews the current evidence for targeted therapies in advanced colorectal cancer, including up-to-date data regarding anti-epidermal growth factor receptor (EGFR) and anti-vascular endothelial growth factor (VEGF) agents, the relevance of primary tumor location and novel subgroups such as BRAF mutated, HER2 amplified, and mismatch-repair-deficient cancers. Expert commentary: EGFR-targeted and VEGF-targeted antibodies are now routinely incorporated into treatment strategies for metastatic colorectal cancer (mCRC). The use of EGFR-targeted antibodies should be restricted to patients with extended RAS wild-type profiles, and there is evidence that they should be further restricted to patients with left-sided tumors. Clinically, mCRC can be divided into subgroups based on RAS, BRAF, HER2, and MMR status, each of which have distinct treatment pathways.

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.

Cetuximab retreatment in patients with metastatic colorectal cancer who exhibited a clinical benefit in response to prior cetuximab: A retrospective study

Clinical benefits of cetuximab retreatment in patients with metastatic colorectal (mCRC) have been reported. In the present study, the effect of cetuximab retreatment on predictive markers was investigated by evaluating the clinical benefit of initial cetuximab treatment prior to cetuximab retreatment. Between November 2012 and March 2017, 14 patients with KRAS proto-oncogene GTPase exon 2 wild-type mCRC who exhibited a clinical benefit (confirmed stable disease for at least 6 months or a clinical response) to an initial cetuximab-based regimen, who received multiple lines of chemotherapy following disease progression and ultimately received a second cetuximab and irinotecan regimen, were retrospectively analyzed. For retreatment, patients received bi-weekly irinotecan (120-150 mg/m²) combined with cetuximab (400 mg/m² as an initial dose, followed by 250 mg/m², weekly). The median age of the 14 patients (11 males, 3 females) was 68 years (32-77). The median progression-free survival (PFS) following prior cetuximab-based therapy was 6.6 months (range, 4.1-18.4). Initial cetuximab treatment was administered as a first-line treatment in 11 patients, a second-line treatment in 1 patient and a third-line treatment in 2 patients. The median interval time between the last cycle of initial cetuximab-based therapy and the first cycle of cetuximab retreatment was 13.1 months (range, 6.0-37.1). The objective response rate of cetuximab retreatment was 21.4% and the median PFS was 4.4 months (95% confidence interval, 1.4-5.6). The Spearman's correlation coefficient for the PFS following retreatment and duration of initial cetuximab-based regimens demonstrated a more marked correlation compared with that between the PFS following retreatment and the interval time between the two regimens (r=0.45, P=0.11 vs. r=0.08, P=0.79). Cetuximab retreatment may provide clinical benefit to patients with mCRC who were good responders with longer periods of initial cetuximab-based therapy.

Optimising the use of cetuximab in the continuum of care for patients with metastatic colorectal cancer

The anti-epidermal growth factor receptor (EGFR) monoclonal antibody cetuximab in combination with chemotherapy is a standard of care in the first-line treatment of RAS wild-type (wt) metastatic colorectal cancer (mCRC) and has demonstrated efficacy in later lines. Progressive disease (PD) occurs when tumours develop resistance to a therapy, although controversy remains about whether PD on a combination of chemotherapy and targeted agents implies resistance to both components. Here, we propose that some patients may gain additional clinical benefit from the reuse of cetuximab after having PD on regimens including cetuximab in an earlier treatment line. We conducted a non-systematic literature search in PubMed and reviewed published and ongoing clinical trials, focusing on later-line cetuximab reuse in patients with mCRC. Evidence from multiple studies suggests that cetuximab can be an efficacious and tolerable treatment when continued or when fit patients with mCRC are retreated with it after a break from anti-EGFR therapy. Furthermore, on the basis of available preclinical and clinical evidence, we propose that longitudinal monitoring of RAS status may identify patients suitable for such a strategy. Patients who experience progression on cetuximab plus chemotherapy but have maintained RAS wt tumour status may benefit from continuation of cetuximab with a chemotherapy backbone switch because they have probably developed resistance to the chemotherapeutic agents rather than the biologic component of the regimen. Conversely, patients whose disease progresses on cetuximab-based therapy due to drug-selected clonal expansion of RAS-mutant tumour cells may regain sensitivity to cetuximab following a defined break from anti-EGFR therapy. Looking to the future, we propose that RAS status determination at disease progression by liquid, needle or excisional biopsy may identify patients eligible for cetuximab continuation and rechallenge. With this approach, treatment benefit can be extended, adding to established continuum-of-care strategies in patients with mCRC.

Incorporating BEAMing technology as a liquid biopsy into clinical practice for the management of colorectal cancer patients: an expert taskforce review

The importance of mutation identification for advanced colorectal cancer treatment with anti-epidermal growth factor receptor agents is well established. However, due to delays in turnaround time, low-quality tissue samples, and/or lack of standardization of testing methods a significant proportion of patients are being treated without the information that Kirsten rat sarcoma and neuroblastoma rat sarcoma (RAS) testing can provide. The detection of mutated circulating tumor DNA by BEAMing technology addresses this gap in care and allows these patients to receive international guideline-recommended expanded RAS testing with rapid turnaround times. Furthermore, the overall concordance between OncoBEAM RAS colorectal cancer testing and standard of care tissue testing is very high (93.3%). This article presents an overview of the clinical utility and potential applications of this minimally invasive method, such as early detection of emergent resistance to anti-epidermal growth factor receptor therapy. If appropriately implemented, BEAMing technology holds considerable promise to enhance the quality of patient care and improve clinical outcomes.

Emergence of KRAS-mutation in liver metastases after an anti-EGFR treatment in patient with colorectal cancer: Are we aware of the therapeutic impact of intratumor heterogeneity?

Tumors represent a dynamic system where the genomic plasticity permits to adapt to the perturbation induced by environmental pressures, supporting the importance of longitudinal tumor sampling strategies to deciphering the temporal acquisition of driver event that could impact treatment outcome. We describe the case of a metastatic colorectal cancer (mCRC) patient, RAS wild-type, who responded to anti-EGFR therapy and underwent liver surgery, revealing a KRAS mutations in the metastatic lesion, not detectable prior to initiation of therapy in the colonic biopsy. After liver surgery, the patient received chemotherapy alone, then underwent left colectomy and the final pathological report confirmed the KRAS wild-type status. We can speculate the existence of two distinct populations of KRAS wild-type and mutant CRC cells sharing the same genetic origin. The anti-EGFR treatment represented a selective pressure which allowed the selection of KRAS mutant subclones. The prognostic and /or predictive role of intratumor heterogeneity has not been assessed prospectively. Our case report is of clinical relevance because patients with mCRC who respond to anti-EGFR antibodies often develop resistance within several months of initiating therapy, thus outlining the importance to better ascertain the molecular landscape of tumors to design better therapeutic strategies.

Beyond second-line therapy in patients with metastatic colorectal cancer: a systematic review

Background

The optimal chemotherapeutic regimen for use beyond the second line for patients with metastatic colorectal cancer (mCRC) remains unclear.

Materials and methods

We systematically searched the Cochrane Database of Systematic Reviews, EMBASE and Medline for records published between January 2002 and May 2017, and cancer congress databases for records published between January 2014 and June 2017. Eligible studies evaluated the efficacy, safety and patient-reported outcomes of monotherapies or combination therapies at any dose and number of treatment cycles for use beyond the second line in patients with mCRC. Studies were assessed for design and quality, and a qualitative data synthesis was conducted to understand the impact of treatment on overall survival and other relevant cancer-related outcomes.

Results

The search yielded 938 references of which 68 were included for qualitative synthesis. There was limited evidence to support rechallenge with chemotherapy, targeted therapy or both. Compared with placebo, an overall survival benefit for trifluridine/tipiracil (also known as TAS-102) or regorafenib has been shown for patients previously treated with conventional chemotherapy and targeted therapy. There was no evidence to suggest a difference in efficacy between these treatments. Patient choice and quality of life at this stage of treatment should also be considered when choosing an appropriate therapy.

Conclusions

These findings support the introduction of an approved agent such as trifluridine/tipiracil or regorafenib beyond the second line before any rechallenge in patients with mCRC who have failed second-line treatment.

Significance of Liquid Biopsy for Monitoring and Therapy Decision of Colorectal Cancer

PURPOSE

Despite therapeutic improvements, all patients with nonresectable metastatic colorectal cancer (mCRC) acquire resistance to treatment probably due to the growth of mutated clones. In contrast to tissue-based studies, liquid biopsies have enabled the opportunity to reveal emerging resistance to treatment by detecting mutated clones and noninvasively monitoring clonal dynamics during therapy.

METHODS

The courses of three patients with mCRC who were initially RAS wild-type were monitored longitudinally using liquid biopsy with long-term follow-up of up to 20 sequential samples. Detection of fragmented RAS mutated circulating cell-free DNA (cf)DNA in plasma was performed by BEAMing. In addition, plasma digital droplet PCR was used to detect and quantify BRAF and PIK3CA mutated cfDNA. Changes of mutational load were correlated with imaging data.

RESULTS

A combination of liquid biopsy and radiological imaging enabled visualization of the occurrence of clonal redistribution after discontinuation of anti-EGFR mAb therapy, as well as emerging RAS mutations during therapy with anti-EGFR mAb indicating resistance. Furthermore, we found that growth of RAS mutated clones is independent of direct selective pressure by anti-EGFR therapy, which is a significant and new finding of this study.

CONCLUSIONS

Our findings demonstrated the whole spectrum of clonal selection and redistribution of mutated cell clones leading to acquired resistance. Given our observation that the growth of RAS mutated clones can evolve even in the absence of anti-EGFR mAb therapy, there is a clear imperative to monitor RAS mutations in serial blood draws in all RAS wild-type patients in general and independent of the therapy.

Propensity Score Analysis of Regorafenib Versus Trifluridine/Tipiracil in Patients with Metastatic Colorectal Cancer Refractory to Standard Chemotherapy (REGOTAS): A Japanese Society for Cancer of the Colon and Rectum Multicenter Observational Study

BACKGROUND

This study compared the efficacy of regorafenib and trifluridine/tipiracil (TFTD) in patients with metastatic colorectal cancer (mCRC) who are refractory to standard chemotherapy, because despite their clinical approval, it still remains unclear which of these two drugs should be used as initial treatment.

MATERIALS AND METHODS

The clinical data of patients with mCRC who were treated with regorafenib or TFTD and those of drug-naive patients, between June 2014 and September 2015, were retrospectively collected from 24 institutions in Japan. Overall survival (OS) was evaluated using the Cox's proportional hazard models based on propensity score adjustment for baseline characteristics.

RESULTS

A total of 550 patients (223 patients in the regorafenib group and 327 patients in the TFTD group) met all criteria. The median OS was 7.9 months (95% confidence interval [CI], 6.8-9.2) in the regorafenib group and 7.4 months (95% CI, 6.6-8.3) in the TFTD group. The propensity score adjusted analysis showed that OS was similar between the two groups (adjusted hazard ratio [HR], 0.96; 95% CI, 0.78-1.18). In the subgroup analysis, a significant interaction with age was observed. Regorafenib showed favorable survival in patients aged <65 years (HR, 1.29; 95% CI, 0.98-1.69), whereas TFTD was favored in patients aged ≥65 years (HR, 0.78; 95% CI, 0.59-1.03).

CONCLUSION

No significant difference in OS between regorafenib and TFTD was observed in patients with mCRC. Although the choice of the drug by age might affect survival, a clearly predictive biomarker to distinguish the two drugs should be identified in further studies.

IMPLICATIONS FOR PRACTICE

Previous studies of patients with metastatic colorectal cancer refractory to standard chemotherapy had demonstrated that both regorafenib and trifluridine/tipiracil could result in increased overall survival compared with placebo, but there are no head-to-head trials. This large, multicenter, observational study retrospectively compared the efficacy of regorafenib and trifluridine/tipiracil in 550 patients with metastatic colorectal cancer refractory to standard chemotherapy who had access to both drugs. Although no difference in overall survival was found between the two drugs in adjusted analysis using propensity score, regorafenib showed favorable survival in patients aged <65 years, whereas trifluridine/tipiracil was favored in patients aged ≥65 years in the subgroup analysis.

Redefining Later-Line Therapy in Metastatic Colorectal Cancer

Colorectal cancer (CRC) is the third most commonly diagnosed malignancy and the fourth leading cause of cancer death in the world, accounting for approximately 1.4 million new cases and almost 700,000 deaths in 2012.1 The objective of the symposium was to provide an overview of the current treatment landscape in terms of later-line therapy in metastatic CRC (mCRC) and to discuss the evidence for the various options available, including rechallenge and therapies such as trifluridine (FTD)/tipiracil (TPI) (Lonsurf®; also known as TAS-102) and regorafenib (Stivarga®). The symposium started by examining the clinical value of third-line treatment in patients with mCRC and providing an insight into the mechanism of action of FTD/TPI, and a comparison with that of 5-fluorouracil (5-FU). The safety and efficacy of FTD/ TPI was then discussed together with the practical management of patients on treatment. The speakers tackled the issue of rechallenge and reintroduction as an option in the third-line, reviewing the pros and cons, and the available studies providing information on the safety and efficacy of the different options in later lines, concluding that there is a lack of robust evidence for rechallenge as a clinical decision. This was followed by a review of the compelling evidence for the use of treatments such as FTD/TPI and regorafenib in the third-line, with documented evidence for efficacy.

REOX: Evaluation of the Efficacy of Retreatment With an Oxaliplatin-containing Regimen in Metastatic Colorectal Cancer: A Retrospective Single-center Study

BACKGROUND

Treatment of metastatic colorectal adenocarcinoma (mCRC) has evolved, and survival is over 30 months in contemporary trials. Nevertheless, there is a paucity of effective regimes after the first or second-line treatment. Thus, reexposure to previously used drugs has become a treatment strategy for some patients. We aimed to evaluate the efficacy of retreatment with an oxaliplatin-containing regimen in mCRC and correlate this with clinicopathologic features.

PATIENTS AND METHODS

We retrospectively analyzed 83 patients with mCRC who underwent reexposure to oxaliplatin (REOX). REOX was defined as a second trial of an oxaliplatin-containing regimen after a previous failure. Primary endpoint was time to treatment failure (TTF).

RESULTS

The median age was 53.5 years, and the female/male ratio was 51.8%/48.2%. The site of the primary tumor was colon (67.5%) and rectal (32.5%). KRAS was mutated in 39.8%. Liver-limited metastasis was found in 19.3% of patients. The main regimen was 5-fluorouracil, levoleucovorin, and oxaliplatin (mFOLFOX6) (84.3%). Bevacizumab and cetuximab were used in 42.2% and 6% of patients, respectively. REOX was used in the third and fourth lines in 48.2% and 25.3% of patients, respectively. The median TTF after REOX was 6.04 months. Overall survival (OS) was 10.04 months. Disease control (complete response + partial response + stable disease) was observed in 56.6%, whereas 42.2% had progressive disease. Partial response + complete response to previous oxaliplatin was predictive of prolonged OS. Patients who attained disease control had better median OS compared with those with progressive disease (14.5 vs. 6.24 months; P < .0001).

CONCLUSION

In the setting of heavily pretreated patients with mCRC, REOX was an effective treatment, with mTTF of 6.04 months in our cohort. Selection of patients with the longest time since previous oxaliplatin can translate in better outcome. Further studies should be conducted to confirm our data.

Rechallenge and maintenance therapy using cetuximab and chemotherapy administered to a patient with metastatic colorectal cancer

Background

Cetuximab combined with chemotherapy is one of the first-line treatments of metastatic colorectal cancer. Although disease progression inevitably occurs, rechallenge and maintenance therapies using cetuximab-based regimens may be beneficial, particularly for patients with wild-type (WT) KRAS.

Case presentation

A 47-year-old female patient who underwent right hemicolectomy presented with an ulcerative adenocarcinoma (grade 2) revealed by histopathological analysis. The patient received three cycles of adjuvant chemotherapy, but disease recurred 15 months later. Cetuximab and a FOLFOX-4 regimen were administered, followed by surgery and adjuvant chemotherapy that was administered for approximately one year. Three years after completing adjuvant therapy, her serum carcinoembryonic antigen levels rapidly increased, and enhanced computed tomography showed widespread metastases. Rechallenge with cetuximab and the FOLFIRI regimen was then initiated, and after 12 cycles, lesions in the lung and liver shrank significantly, and serum CEA levels dramatically declined. Maintenance therapy with cetuximab and capecitabine was then administered for 10 months until the metastatic lesions in the lung and liver enlarged.

Conclusion

Rechallenge and maintenance therapy with cetuximab-based chemotherapy were relatively effective for managing a female patient with WT KRAS. Optimization of this strategy requires further in-depth investigations of more patients.

Clinical Application of Liquid Biopsy in Targeted Therapy of Metastatic Colorectal Cancer

Background. Colorectal cancers (CRC) shed DNA into blood circulation. There is growing evidence that the analysis of circulating tumor DNA can be effectively used for monitoring of disease, to track tumor heterogeneity and to evaluate response to treatment. Case Presentation. Here, we describe two cases of patients with advanced CRC. The first case is about a patient with no available tissue for analysis of RAS mutation status. Liquid biopsy revealed RAS-wild-type and the therapy with anti-EGFR (epidermal growth factor receptor) monoclonal antibody cetuximab could be initiated. In the second case, the mutational profile of a patient with initial wild-type RAS-status was continually tracked during the course of treatment. An acquired KRAS exon 3 mutation was detected. The number of KRAS mutated fragments decreased continuously after the discontinuation of the therapy with EGFR-specific antibodies. Conclusion. Liquid biopsy provides a rapid genotype result, which accurately reproduces the current mutation status of tumor tissue. Furthermore, liquid biopsy enables close monitoring of the onset of secondary resistance to anti-EGFR therapy.

Chemotherapy rechallenge after regorafenib treatment in metastatic colorectal cancer: still hope after the last hope?

INTRODUCTION

The introduction of biological agents in cancer therapy is changing the progression of metastatic colorectal cancer. Currently, resistance to biological agents is an emerging problem; the progression of the disease is caused by the development of resistant clones. According to some authors, these clones can be re-sensitized to traditional and previously utilized chemotherapy agents. The results of the CORRECT study demonstrated the efficacy of regorafenib monotherapy in both KRAS wild type and mutant pretreated patients (pts). Two recent reports showed the potential of reintroduction of chemotherapy, even after treatment with regorafenib.

PATIENTS AND METHODS

We performed a retrospective review of clinical data from patients treated with regorafenib at our institution between March 2012 and March 2013. We analysed patient characteristics, KRAS/NRAS status, response to treatment (evaluated by RECIST v1.1 criteria) and survival.

RESULTS

Regorafenib was administered to 128 patients, and 11 (8.6%) received post-regorafenib therapy (to our knowledge). Seven (63.6%) patients were wild type for KRAS/NRAS. Post-regorafenib therapy represented for all the patients at least the fourth line: all the pts received both oxaliplatin- and irinotecan-based chemotherapy, all of them were treated with bevacizumab, and 7 patients also received cetuximab. Eight patients (72.7%) were treated with standard chemotherapy after regorafenib (irinotecan monotherapy, capecitabine plus oxaliplatin or irinotecan, dacarbazine or raltitrexed), while 3 patients received an experimental therapy (clinical trial). Nine of the 11 (81.8%) patients had PD and 2 patients had SD. The median progression-free survival was 1.6+ months (range 0.5-3.5), the median OS post-regorafenib was 2.1+ months (range 0.5-10.2) and the 6-month OS was 27.3%.

CONCLUSION

Our retrospective analysis showed that after regorafenib therapy, re-introduction of chemotherapy is possible. Unfortunately, we reported a high percentage of disease progression beyond regorafenib, which is likely due to the high percentage of heavily pretreated patients (some received four or five types of therapy before regorafenib). We think that regorafenib could represent a chemotherapy resensitizing agent; however, additional studies are needed in patients who have received less pretreatment.

Overcoming dynamic molecular heterogeneity in metastatic colorectal cancer: Multikinase inhibition with regorafenib and the case of rechallenge with anti-EGFR

In metastatic colorectal cancer (mCRC), fluorouracil-based combination therapy with oxaliplatin or irinotecan is the mainstay of first-line treatment. Patient survival has been significantly improved with the introduction of monoclonal antibodies against VEGF (bevacizumab), VEGFR2 (ramucirumab) or EGFR (cetuximab or panitumumab) in first- and second-line therapies. However, all patients treated with chemotherapy and targeted therapies will eventually relapse, and recently the emergence of alterations in EGFR, RAS, BRAF, ERB-B2, MET and possibly in other genes has been shown to jeopardize response to EGFR blockade. In chemorefractory patients, multikinase inhibition with regorafenib has proved to be effective and rechallenge with chemotherapy or anti-EGFR agents is empirically pursued. This review will critically discuss how the evolving knowledge of mechanisms of resistance driven by intratumoural dynamic molecular heterogeneity can impact on rational choice of treatments in this setting.

New findings on primary and acquired resistance to anti-EGFR therapy in metastatic colorectal cancer: do all roads lead to RAS?

Anti-epidermal growth factor receptor therapy with the monoclonal antibodies cetuximab and panitumumab is the main targeted treatment to combine with standard chemotherapy for metastatic colorectal cancer. Many clinical studies have shown the benefit of the addition of these agents for patients without mutations in the EGFR pathway. Many biomarkers, including KRAS and NRAS mutations, BRAF mutations, PIK3CA mutations, PTEN loss, AREG and EREG expression, and HER-2 amplification have already been identified to select responders to anti-EGFR agents. Among these alterations KRAS and NRAS mutations are currently recognized as the best predictive factors for primary resistance. Liquid biopsy, which helps to isolate circulating tumor DNA, is an innovative method to study both primary and acquired resistance to anti-EGFR monoclonal antibodies. However, high-sensitivity techniques should be used to enable the identification of a wide set of gene mutations related to resistance.

Treatment of Metastatic Colorectal Cancer: Standard of Care and Future Perspectives

Palliative chemotherapy for metastatic colorectal cancer has undergone substantial changes in recent years. The implementation of modern biologicals in the treatment has substantially improved overall survival up to 30 months. With the increasing number of therapeutic options, the question of optimal treatment sequence arises, which is addressed in current studies like FIRE 4 or STRATEGIC-1. Furthermore, clinical and molecular biomarkers to predict efficacy and tolerability are urgently needed. Today, the detection of activating RAS mutations is the only validated biomarker which precludes patients from anti-EGFR treatment. The detection of BRAF mutation V600E is associated with a very poor prognosis corresponding to a survival of 9-12 months. Prospective trials evaluating an optimal approach to this subgroup are still missing. First results from strategies targeting the aberrant signal transduction are promising and require further validation. Despite the advances so far, life expectancy unfortunately continues to be limited in the majority of patients with metastatic colorectal cancer. New strategies are needed to improve the prognosis. To this end, the identification of Her2/neu as a potential target and first experiences with checkpoint inhibition in patients with mismatch repair-deficient tumors are promising and also require further validation.

Sym004: Truly a New Level of Anti-EGFR Treatment?

Sym004 is a new antibody mixture to target EGFR in metastatic colorectal cancer. Preclinical data suggest efficacy in anti-EGFR-resistant tumors, but it remains unclear whether a higher toxicity is outweighed by those advantages.

Colorectal cancer: Overcoming resistance to anti-EGFR therapy - where do we stand?

In the past few years, the mechanisms leading to an acquired resistance to anti-EGFR monoclonal antibodies became an important topic in metastatic colorectal cancer research. In this commentary, we briefly summarize the latest update to this field by Arena and colleagues, and discuss promising new drugs and treatment strategies that might lead to overcoming secondary resistance.

Cetuximab Rechallenge and Monotherapy in Patients with Squamous Cell Carcinoma of the Head and Neck

Smokers with squamous cell carcinoma of the head and neck (SCCHN) have a particularly poor prognosis when compared with human papillomavirus-positive SCCHN. Here, we present case reports of two smokers with SCCHN treated with cetuximab-based therapy, highlighting the potential benefit of cetuximab before definitive chemoradiotherapy in patients with poor performance status as well as cetuximab rechallenge after progression. We conclude that cetuximab demonstrated notable effectiveness in two patients at high risk for poor prognosis, yielding a durable response in one and retaining activity on rechallenge in the other.

Pharmacokinetic and pharmacodynamic evaluation of panitumumab in the treatment of colorectal cancer

INTRODUCTION

Integration of targeted therapy and additional chemotherapy options has improved median overall survival (OS) in patients with unresectable metastatic colorectal cancer (mCRC). Cetuximab and panitumumab are examples of targeted therapies, specifically against the epidermal growth factor receptor (EGFR). This review focuses on Panitumumab, a fully human IgG2 monoclonal antibody, which inhibits key oncogenic downstream cell signalling pathways. Panitumumab and cetuximab have improved tumour response rate, progression-free survival, and OS in mCRC patients in whom the RAS (Rat Sarcoma) gene is of Wild Type (WT) status.

AREAS COVERED

The EGFR signalling pathway and preclinical, Phase I and Phase II clinical studies on the pharmacokinetic, pharmacodynamic and safety evaluation of panitumumab are presented. Phase III studies utilising panitumumab in the first, second and third line setting in mCRC are also described.

EXPERT OPINION

Panitumumab exhibits excellent pharmacokinetics and pharmacodynamics by way of uncomplicated dosing, non-existent drug interactions, minimal infusion reactions and manageable side effects, making it a suitable target for combination treatments. However, innate and acquired resistances are still obstacles. To overcome this, experimented strategies are ongoing, particularly in patients with Her-2 and BRAF gene alterations. Novel biomarkers to improve patient selection and second-generation targeted antibodies are in development.

Retreatment with anti-EGFR based therapies in metastatic colorectal cancer: impact of intervening time interval and prior anti-EGFR response

BACKGROUND

This retrospective study aims to investigate the activity of retreatment with anti-EGFR-based therapies in order to explore the concept of clonal evolution by evaluating the impact of prior activity and intervening time interval.

METHODS

Eighty-nine KRAS exon 2-wild-type metastatic colorectal patients were retreated on phase I/II clinical trials containing anti-EGFR therapies after progressing on prior cetuximab or panitumumab. Response on prior anti-EGFR therapy was defined retrospectively per physician-records as response or stable disease ≥6 months. Multivariable statistical methods included a multiple logistic regression model for response, and Cox proportional hazards model for progression-free survival.

RESULTS

Retreatment anti-EGFR agents were cetuximab (n = 76) or cetuximab plus erlotinib (n = 13). The median interval time between prior and retreatment regimens was 4.57 months (range: 0.46-58.7). Patients who responded to the prior cetuximab or panitumumab were more likely to obtain clinical benefit to the retreatment compared to the non-responders in both univariate (p = 0.007) and multivariate analyses (OR: 3.38, 95 % CI: 1.27, 9.31, p = 0.019). The clinical benefit rate on retreatment also showed a marginally significant association with interval time between the two anti-EGFR based therapies (p = 0.053). Median progression-free survival on retreatment was increased in prior responders (4.9 months, 95 % CI: 3.6, 6.2) compared to prior non-responders (2.5 months, 95 % CI, 1.58, 3.42) in univariate (p = 0.064) and multivariate analysis (HR: 0.70, 95 % CI: 0.43-1.15, p = 0.156).

CONCLUSION

Our data lends support to the concept of clonal evolution, though the clinical impact appears less robust than previously reported. Further work to determine which patients benefit from retreatment post progression is needed.

Palliative oxaliplatin-based chemotherapy after exposure to oxaliplatin in the adjuvant setting for colon cancer

BACKGROUND

Little is known regarding the efficacy of oxaliplatin-based chemotherapy for metastatic colon cancer patients who have already received adjuvant oxaliplatin-based chemotherapy.

METHODS

We retrospectively reviewed 22 consecutive patients who developed recurrence after adjuvant oxaliplatin-based chemotherapy for stage III colon cancer and received another course of oxaliplatin-based chemotherapy for their metastatic disease. The main endpoint was progression-free survival (PFS).

RESULTS

A total of 635 patients received oxaliplatin-based chemotherapy for stage III colon cancer at the British Columbia Cancer Agency from 2006 to 2011. A total of 176 patients recurred, 22 (12.5%) of whom were re-exposed to oxaliplatin in the metastatic scenario. Oxaliplatin in combination with fluoropyrimidine was given as first, second and third line in in 3 (13.6%), 14 (63.6%), and 5 (22.7%) patients respectively. Median time from the last cycle of adjuvant oxaliplatin-based chemotherapy to the first cycle of palliative oxaliplatin-based chemotherapy was 44.3 months. Median PFS and overall survival (OS) were 3.3 (95% CI, 1.4-5.1) and 10.0 months (95% CI, 5.3-14.6), respectively. There was no difference in PFS for patients re-exposed to oxaliplatin less than 36 months compared to longer (3.6 versus 3.1 months, P=0.793, HR =0.88).

CONCLUSIONS

In this population-based study, only a small proportion of pts who recurred after oxaliplatin-based adjuvant therapy received oxaliplatin in the metastatic setting. Re-exposure of oxaliplatin in combination with fluoropyrimidine is associated with only modest PFS benefit. Larger studies evaluating the role of oxaliplatin re-exposure are needed.

Emerging drugs in refractory colorectal cancer

Colorectal cancer is the third leading cause of cancer-related deaths in the western world. Despite therapeutic advances, the prognosis of metastatic colorectal cancer patients remains poor due to intrinsic or acquired tumor drug resistance. The main mechanisms of tumor drug resistance are represented by genetic and epigenetic alterations. This leads to tumor refractoriness during treatment or disease progression following response to first-line therapy. Strategies to combat chemorefractory tumors involve the development of selective inhibitors of drug-resistant phenotypes, the epigenetic resensitization of drug-resistant cancer cells and new cytotoxic drugs devoid of cross resistance with first-line cytotoxics. The use of drug combination regimens may also increase treatment efficacy, and the exploitation of specific phenomena such as oncogenic and nononcogenic addiction or synthetic lethality represents another potential approach in combating tumor drug resistance. Clinical trials based on such strategies in mCRC patients whose tumors progressed following first-line chemotherapy are discussed herein.

Characterizing the patterns of clonal selection in circulating tumor DNA from patients with colorectal cancer refractory to anti-EGFR treatment

INTRODUCTION

KRAS and EGFR ectodomain-acquired mutations in patients with metastatic colorectal cancer (mCRC) have been correlated with acquired resistance to anti-EGFR monoclonal antibodies (mAbs). We investigated the frequency, co-occurrence, and distribution of acquired KRAS and EGFR mutations in patients with mCRC refractory to anti-EGFR mAbs using circulating tumor DNA (ctDNA).

PATIENTS AND METHODS

Sixty-two post-treatment plasma and 20 matching pretreatment archival tissue samples from KRAS (wt) mCRC patients refractory to anti-EGFR mAbs were evaluated by high-sensitivity emulsion polymerase chain reaction for KRAS codon 12, 13, 61, and 146 and EGFR 492 mutations.

RESULTS

Plasma analyses showed newly detectable EGFR and KRAS mutations in 5/62 [8%; 95% confidence interval (CI) 0.02-0.18] and 27/62 (44%; 95% CI 0.3-0.56) samples, respectively. KRAS codon 61 and 146 mutations were predominant (33% and 11%, respectively), and multiple EGFR and/or KRAS mutations were detected in 11/27 (41%) cases. The percentage of mutant allele reads was inversely correlated with time since last treatment with EGFR mAbs (P = 0.038). In the matching archival tissue, these mutations were detectable as low-allele-frequency clones in 35% of patients with plasma mutations after treatment with anti-EGFR mAbs and correlated with shorter progression-free survival (PFS) compared with the cases with no new mutations (3.0 versus 8.0 months, P = 0.0004).

CONCLUSION

Newly detected KRAS and/or EGFR mutations in plasma ctDNA from patients refractory to anti-EGFR treatment appear to derive from rare, pre-existing clones in the primary tumors. These rare clones were associated with shorter PFS in patients receiving anti-EGFR treatment. Multiple simultaneous mutations in KRAS and EGFR in the ctDNA and the decline in allele frequency after discontinuation of anti-EGFR therapy in a subset of patients suggest that several resistance mechanisms can co-exist and that relative clonal burdens may change over time. Monitoring treatment-induced genetic alterations by sequencing ctDNA could identify biomarkers for treatment screening in anti-EGFR-refractory patients.

Biologic therapies in colorectal cancer: indications and contraindications

The role of antiangiogenic and anti-epidermal growth factor receptor (EGFR) agents has been investigated extensively in colorectal cancer in the palliative, adjuvant, and neoadjuvant settings. Although the role of biologic agents has become well-defined in the first, second, and subsequent lines of treatment of metastatic colorectal cancer (mCRC), considerable debate continues around the optimal sequencing and around optimal patient selection. The benefits from integrating bevacizumab or cetuximab in the adjuvant setting have been investigated in several randomized phase III clinical trials in stage II/III disease, all with disappointing results. Neoadjuvant approaches incorporating biologic therapy in patients with liver metastatic disease have led to mixed results. Although the current evidence does suggest increased down-staging and increased resectability with the addition of cetuximab in patients with initially unresectable or borderline resectable liver metastases, a positive effect of anti-EGFR therapy on the overall survival (OS) in this setting is not conclusive. Patients with resectable liver metastases derive no benefit and may experience potential harm from the addition of cetuximab to neoadjuvant chemotherapy. Similarly, there is neither rationale nor adequate data to support the addition of bevacizumab to neoadjuvant chemotherapy in patients with resectable liver metastases. In this review, we examine the role of antiangiogenesis and anti-EGFR therapies across the spectrum of adjuvant, neoadjuvant, and metastatic disease.

The role of targeted therapy for gastrointestinal tumors

Many targeted drugs have been studied to target the molecular pathways involved in the development of gastrointestinal cancers. Anti-VEGF, anti-EGFR agents, and recently also multi-kinase inhibitor regorafenib, have already been available for the treatment of metastatic colorectal cancer patients. To date, Her-2 positive, gastric cancer patients, are also treated with trastuzumab, while the multi-targeted inhibitor, sorafenib, represents the standard treatment for hepatocellular carcinoma patients. Finally, sunitinib and everolimus, have been approved for the treatment of the neuroendocrine gastroenteropancreatic tumors. Actually a great number of further drugs are under preclinical and clinical development. The aim of this review is to provide a comprehensive overview of the state of art, focusing on the new emerging strategies in the personalized treatment of gastrointestinal tumors.

[Chemotherapy of metastatic colorectal cancer]

Increasing numbers of therapeutic options are becoming available for the systemic treatment of metastasized colorectal cancer (mCRC) which emphasizes the need for strategic decision making and planning across multiple lines of treatment. The choice of first-line therapy is influenced by clinical and molecular characteristics of patients and tumors, such as (K-)RAS gene mutations with respect to therapy guidance of epidermal growth factor receptor (EGFR) antibodies. First-line therapy is the major determinant of subsequent treatment regimens and can therefore be considered as the key decision in patients with mCRC. The German standard for first-line therapy in the majority of patients includes chemotherapy in combination with biological agents, with antibodies targeting EGFR possibly being the preferable option in patients with (K-)RAS wild-type tumors. The development of effective therapeutic strategies in patients with (K-)RAS mutant mCRC tumors must be promoted in the future and requires intensive research because the therapy options for this group of patients are very limited.

FOLFIRINOX bevacizumab is a promising therapy for chemorefractory metastatic colorectal cancer

PURPOSE

Fluoropyrimidines, oxaliplatin, irinotecan and targeted therapies represent the standard treatment of metastatic colorectal cancer. After failure of all these treatments, few options are available. In such chemorefractory patients the effect of triplet chemotherapy with bevacizumab (FOLFIRINOX bevacizumab) has never been investigated.

PATIENTS AND METHODS

49 consecutive patients bearing unresectable metastatic colorectal cancer and who experienced failure to oxaliplatin- and irinotecan-based chemotherapy were treated with oxaliplatin (85 mg/m(2)), irinotecan (180 mg/m(2)), leucovorin (400 mg/m(2)), and fluorouracil (400 mg/m(2) bolus then 2,400 mg/m(2)) repeated every 2 weeks.

RESULTS

Median age was 63 (range 36-82) years. After a median follow-up of 12 months, the median progression-free survival was 5.8 months (95% CI 3.4-6.8) and the median overall survival was 11.9 months (95% CI 8-18). The response rate after the cycle was evaluable for 36 patients, whereby we observed 18% (95% CI 8-35) partial or complete response, 45% (95% CI 28-68) stable disease of more than 2 months, and 37% (95% CI 21-58) progression.

CONCLUSION

This study suggests that bevacizumab + FOLFIRINOX may be active in mCRC patients after failure of classical lines of chemotherapy.

TGFα and amphiregulin paracrine network promotes resistance to EGFR blockade in colorectal cancer cells

PURPOSE

Targeted inhibition of EGFR with the mAbs cetuximab or panitumumab is a valuable treatment for RAS wild-type colorectal cancers. The efficacy of EGFR blockade is limited by the emergence of acquired resistance often attributed to secondary KRAS mutations. Remarkably, tumor biopsies from resistant patients show that only a fraction of the resilient cells carry KRAS mutations. We hypothesized that a paracrine cross-talk driven by the resistant subpopulation may provide in trans protection of surrounding sensitive cells.

EXPERIMENTAL DESIGN

Conditioned medium assays and three-dimensional cocultures were used to assess paracrine networks between cetuximab-sensitive and -resistant cells. Production of EGFR ligands by cells sensitive to cetuximab and panitumumab was measured. The ability of recombinant EGFR ligands to protect sensitive cells from cetuximab was assessed. Biochemical activation of the EGFR signaling pathway was measured by Western blotting.

RESULTS

Colorectal cancer cells sensitive to EGFR blockade can successfully grow despite cetuximab treatment when in the company of their resistant derivatives. Media conditioned by resistant cells protect sensitive parental cells from cetuximab. EGFR blockade triggers increased secretion of TGFα and amphiregulin. Increased secretion of ligands by resistant cells can sustain EGFR/ERK signaling in sensitive cells.

CONCLUSIONS

Colorectal cancer cells that develop resistance to cetuximab and panitumumab secrete TGFα and amphiregulin, which protect the surrounding cells from EGFR blockade. This paracrine protective mechanism might be therapeutically exploitable.

How to find the Ariadne's thread in the labyrinth of salvage treatment options for metastatic colorectal cancer?

Since a chance for cure was found out in metastatic colorectal cancer (mCRC) patients undergoing a resection of liver and lung metastases, high tumor shrinkage by chemotherapy regimens and their combination with targeted agents have been addressed in potentially resectable mCRC. However, most mCRC patients cannot reach this opportunity because of tumor burden or metastatic sites. For these patients a salvage systemic therapy could be offered to prolong survival. To date, a huge number of clinical trials provided some evidences for the achievement of this goal. A lot of chemotherapeutic regimens in combination with biological therapies are now available. We tried to propose a simple way to choose the best options and to plan an optimal sequence of treatments. This tool could help the oncologists worldwide to better and easily manage mCRC patients who need salvage systemic therapy.

A systematic review of salvage therapy to patients with metastatic colorectal cancer previously treated with fluorouracil, oxaliplatin and irinotecan +/- targeted therapy

Oxaliplatin, irinotecan and 5-fluorouracil in combination with or without targeted therapies are well-documented treatment options for first- and second-line treatments of metastatic colorectal cancer. However, there are much less data on the beneficial effect on systemic therapy in the third-line setting. We therefore performed a systematic review of the current literature on third or later lines of treatment to patients with metastatic colorectal cancer after the use of approved drugs or combinations.

METHODS

A computer-based literature search was carried out using Pubmed and data reported at international meetings. Original studies reporting ≥15 patients who had previously received 5-fluorouracil, oxaliplatin and irinotecan were included. Furthermore, patients with KRAS wild type tumours should had received EGFR-directed therapy.

RESULTS

Conventional chemotherapeutic agents as capecitabine, mitomycin C, and gemcitabine have limited or no activity. Retreatment with oxaliplatin might be an option in selected patients. In addition, rechallenge with EGFR-directed therapy might be a valuable strategy. Data also suggest that angiogenetic drugs may postpone further progression and prolong survival. Lately, regorafinib has been approved. In conclusion, our current knowledge is based on many retrospective studies, some phase II studies and very few randomized clinical trials. Further prospective phase III trials comparing an investigational drug or combination with best supportive care in third- or later lines of treatment in metastatic colorectal cancer are highly warranted. Identification of predictive biomarkers and improvement of our understanding of molecular mechanisms is crucial.

Options for metastatic colorectal cancer beyond the second line of treatment

Colorectal cancer is the third most common cancer, with recent advances in the management of unresectable metastatic lesions. The aim of this review is to discuss the remaining options for heavily pretreated patients with unresectable metastatic colorectal cancer. Beyond second-line treatment, two epidermal growth factor receptor (EGFR) inhibitors, cetuximab and panitumumab, have a demonstrated clinical interest in patients with KRAS wild-type tumours. However, few data exist in patients pretreated with an anti-EFGR and who are being rechallenged with anti-EGFR drugs. Reintroduction of chemotherapy should be considered. In September 2012, regorafenib, a multi-kinase inhibitor was approved by the US Federal Drug Administration for patients refractory to other standard treatments. In the case of metastases limited to the liver, transarterial chemoembolization, hepatic artery infusion and radioembolization could also be discussed in selected patients. With the multiplication of therapeutic options in first-line, second-line treatment, and beyond, the concept of subsequent lines of chemotherapy should be replaced by a multiline strategy, dependent on the patient and on tumour biology. A better understanding of the tumour biology and predictive factors for the response to these therapies is needed, and further strategic trials are urgently warranted.

Evidence-based appraisal of the upfront treatment for unresectable metastatic colorectal cancer patients

Colorectal cancer (CRC) is a significant health problem, with around 1 million new cases and 500000 deaths every year worldwide. Over the last two decades, the use of novel therapies and more complex treatment strategies have contributed to progressively increase the median survival of patients with unresectable advanced CRC up to approximately 30 mo. The availability of additional therapeutic options, however, has created new challenges and generated more complicated treatment algorithms. Moreover, several clinically important points are still in debate in first-line, such as the optimal treatment intensity, the most appropriate maintenance strategy, the preferred biologic to be used upfront in patients with KRAS wild-type CRC, and the need for more detailed information on tumor biology. In this moving landscape, this review analyses why the first-line treatment decision is crucial and how the choice may impact on further treatment lines. In addition, it focuses on results of major phase III randomized trials.

The ErbB/HER family of protein-tyrosine kinases and cancer

The human epidermal growth factor receptor (EGFR) family consists of four members that belong to the ErbB lineage of proteins (ErbB1-4). These receptors consist of a glycosylated extracellular domain, a single hydrophobic transmembrane segment, and an intracellular portion with a juxtamembrane segment, a protein kinase domain, and a carboxyterminal tail. Seven ligands bind to EGFR including epidermal growth factor and transforming growth factor α, none bind to ErbB2, two bind to ErbB3, and seven ligands bind to ErbB4. The ErbB proteins function as homo and heterodimers. The heterodimer consisting of ErbB2, which lacks a ligand, and ErbB3, which is kinase impaired, is surprisingly the most robust signaling complex of the ErbB family. Growth factor binding to EGFR induces a large conformational change in the extracellular domain, which leads to the exposure of a dimerization arm in domain II of the extracellular segment. Two ligand-EGFR complexes unite to form a back-to-back dimer in which the ligands are on opposite sides of the aggregate. Following ligand binding, EGFR intracellular kinase domains form an asymmetric homodimer that resembles the heterodimer formed by cyclin and cyclin-dependent kinase. The carboxyterminal lobe of the activator kinase of the dimer interacts with the amino-terminal lobe of the receiver kinase thereby leading to its allosteric stimulation. Downstream ErbB signaling modules include the phosphatidylinositol 3-kinase/Akt (PKB) pathway, the Ras/Raf/MEK/ERK1/2 pathway, and the phospholipase C (PLCγ) pathway. Several malignancies are associated with the mutation or increased expression of members of the ErbB family including lung, breast, stomach, colorectal, head and neck, and pancreatic carcinomas and glioblastoma (a brain tumor). Gefitinib, erlotinib, and afatinib are orally effective protein-kinase targeted quinazoline derivatives that are used in the treatment of ERBB1-mutant lung cancer. Lapatinib is an orally effective quinazoline derivative used in the treatment of ErbB2-overexpressing breast cancer. Trastuzumab, pertuzumab, and ado-trastuzumab emtansine, which are given intravenously, are monoclonal antibodies that target the extracellular domain and are used for the treatment of ErbB2-positive breast cancer; ado-trastuzumab emtansine is an antibody-drug conjugate that delivers a cytotoxic drug to cells overexpressing ErbB2. Cetuximab and panitumumab are monoclonal antibodies that target ErbB1 and are used in the treatment of colorectal cancer. Cancers treated with these targeted drugs eventually become resistant to them. The role of combinations of targeted drugs or targeted drugs with cytotoxic therapies is being explored in an effort to prevent or delay drug resistance in the treatment of these malignancies.

Rechallenge therapy and treatment holiday: different strategies in management of metastatic colorectal cancer

Fluoropyrimidines, oxaliplatin, irinotecan and biologic therapies (Bevacizumab, Panitumumab, and Cetuximab) represent the backbone of metastatic colorectal cancer (CRC) treatment. The improvement in survival for mCRC patient led to two main outstanding issues: 1) there is a significant number of patients progressing beyond the third or fourth line of treatment still suitable for further therapy when enrollment into clinical trial is not possible. In this situation, the role of any therapy rechallenge (either chemotherapy alone, chemotherapy and biologic therapy or biologic therapy alone) is still not clear, particularly in patients who had previously responded, and if treatment choice is based on traditional dogma of primary and secondary resistance, rechallenge does not seem to be justified. 2) Prolonged intensive treatment is burdened from the high risk of cumulative toxicity, worsening in quality of life and a not well defined possibility of early acquired resistance.Different hypothesis could justify the research of different strategy in treatment of mCRC:1) Epigenetic changes might drive resistance and treatment could induce these changes. Re-expression of silenced tumor suppressive genes might resensitize tumors to therapy. It is therefore possible that a drug holiday (intermittent treatment) could allow reversion to a previous epigenetic profile. Moreover an intermittent treatment could delay acquired resistance. 2) It is plausible that tumor grows as a polyclonal mass. If it responds but then becomes resistant to one or more treatments, retreatment might be successful if changing therapies allows to that clone of cells to re-emerge. On these basis, we focused this review on the actual evidences in management of mCRC patients in terms of chemotherapy or biological therapies rechallenge and intermittent treatment. Moreover, we will discuss the potential biological mechanisms of the observed results of early clinical trials.

Drug rechallenge and treatment beyond progression--implications for drug resistance

The established dogma in oncology for managing recurrent or refractory disease dictates that therapy is changed at disease progression, because the cancer is assumed to have become drug-resistant. Drug resistance, whether pre-existing or acquired, is largely thought to be a stable and heritable process; thus, reuse of therapeutic agents that have failed is generally contraindicated. Over the past few decades, clinical evidence has suggested a role for unstable, non-heritable mechanisms of acquired drug resistance pertaining to chemotherapy and targeted agents. There are many examples of circumstances where patients respond to reintroduction of the same therapy (drug rechallenge) after a drug holiday following disease relapse or progression during therapy. Additional, albeit limited, evidence suggests that, in certain circumstances, continuing a therapy beyond disease progression can also have antitumour activity. In this Review, we describe the anticancer agents used in these treatment strategies and discuss the potential mechanisms explaining the apparent tumour re-sensitization with reintroduced or continued therapy. The extensive number of malignancies and drugs that challenge the custom of permanently switching to different drugs at each line of therapy warrants a more in-depth examination of the definitions of disease progression and drug resistance and the resulting implications for patient care.

Methods of overcoming treatment resistance in colorectal cancer

Metastatic colorectal cancer remains a lethal disease with a poor prognosis in the majority of patients. Multiple drug combinations have been developed in recent years that have significantly improved response rates and overall survival however resistance to these drugs is inevitable. Novel agents are currently being developed and participation in clinical trials should be encouraged. In the absence of other treatment options in a patient with good performance status, there is compelling evidence for re-challenging with previously administered agents in different combinations. The aim of this review is to discuss mechanisms of resistance and methods to overcome treatment resistance in patients with metastatic colorectal cancer who are refractory to 5-FU, irinotecan, oxaliplatin, cetuximab and bevacizumab therapy.

Single agent panitumumab in KRAS wild-type metastatic colorectal cancer patients following cetuximab-based regimens: Clinical outcome and biomarkers of efficacy

BACKGROUND

Few data are available outlining outcomes of panitumumab in advanced colorectal cancer patients benefiting from prior cetuximab-based regimens.

PATIENTS AND METHODS

Thirty patients with KRAS wild type metastatic colorectal cancer with clinical benefit from prior cetuximab-based regimens between May 2004 and October 2011 were reviewed at nine Italian Institutions. Inclusion key criteria included interruption of cetuximab for reasons other than progressive disease. Patients were classified according to prior regimens (0 or ≥1), prior response or stabilization, surgery of metastases, and Köhne prognostic score. At the time of subsequent progression, patients were treated with single agent panitumumab until progressive disease, unacceptable toxicity, or consent withdrawal.

RESULTS

Panitumumab obtained 67% disease control rate and 30% objective response rate, with median PFS of 4.2 and median OS of 9.6 mo. Patients with BRAF/NRAS/PI3KCA and KRAS (by mutant enriched technique) wild-type tumors had the best chance of response to panitumumab.

CONCLUSIONS

Single agent panitumumab provided significant clinical benefit in heavily pretreated patients without acquired resistance to prior cetuximab-based regimens.

Epidermal growth factor receptor (EGFR) and KRAS mutations during chemotherapy plus anti-EGFR monoclonal antibody treatment in metastatic colorectal cancer

It is now well established that metastatic colorectal cancer patients without KRAS mutation (codon 12) benefit from treatment with an epidermal growth factor receptor monoclonal antibody (anti-EGFR mAb). Recently, EFGR and KRAS mutations have been shown to exist in patients who developed resistance to anti-EGFR mAb. We analyzed KRAS, BRAF V600E and EGFR S492R mutations in 37 post-anti-EGFR mAb tumor samples from 23 patients treated with chemotherapy plus anti-EGFR mAb. No EGFR S492R mutation was detected. A KRAS mutation was found after anti-EGFR mAb in only one tumor. Our results suggest that acquired EGFR S492R and KRAS mutations do not constitute the main mechanism of resistance to anti-EGFR mAb in combination with chemotherapy.