Clinical, laboratory and molecular factors predicting chemotherapy efficacy and toxicity in colorectal cancer

Colorectal cancer (CRC) treatment has evolved significantly over the last ten years with the use of active chemotherapeutic agents including fluoropyrimidines, oxaliplatin and irinotecan plus targeted monoclonal antibodies bevacizumab, cetuximab and panitumumab. The addition of newer chemotherapeutic agents and targeted therapies has improved patient outcomes at the cost of increased toxicity with not all patients benefiting from these treatments. It is necessary for clinicians to more accurately predict clinical outcomes particularly in the predominantly elderly CRC patient population. This review aims to summarise existing data regarding the use of clinical and laboratory variables plus molecular markers in predicting response, survival and toxicity to chemotherapy agents and targeted monoclonal antibodies currently used in the treatment of CRC.

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 in colon cancer: a marker of resistance to EGFR-I therapy

Introduction and Design

The introduction of the epidermal growth factor receptor inhibitors (EGFR-I) has increased the treatment options available for patients with metastatic colorectal cancer (mCRC). Two EGFR-I agents currently approved for the treatment of mCRC are the fully human monoclonal antibody panitumumab and the mouse-human chimeric monoclonal antibody cetuximab. While these agents have demonstrated activity across multiple lines of therapy, early studies suggested that clinical benefit was confined to a subset of patients treated. Mutation of the KRAS oncogene has emerged as a powerful negative predictive biomarker to identify patients with mCRC who do not benefit from EGFR-I therapy. Multiple retrospective analyses have demonstrated that clinical benefit from treatment with EGFR-I is limited to patients with tumors harboring the wild-type KRAS gene. In this review, the KRAS pathway and studies evaluating KRAS as a prognostic marker in CRC are discussed along with advances in KRAS gene mutation testing. Clinical trials evaluating the role of KRAS status in response to EGFR-I monotherapy or in combination with chemotherapy are also highlighted along with ongoing studies evaluating the role of EGFR-I treatment on curative resections rates.

Results and Conclusion

Future studies investigating EGFR-I therapy in mCRC should incorporate KRAS mutation testing into the study protocol in order to more accurately determine the patient population that will obtain clinical benefit from these novel agents.

Biomarkers predicting clinical outcome of epidermal growth factor receptor-targeted therapy in metastatic colorectal cancer

The monoclonal antibodies panitumumab and cetuximab that target the epidermal growth factor receptor (EGFR) have expanded the range of treatment options for metastatic colorectal cancer. Initial evaluation of these agents as monotherapy in patients with EGFR-expressing chemotherapy-refractory tumors yielded response rates of approximately 10%. The realization that detection of positive EGFR expression by immunostaining does not reliably predict clinical outcome of EGFR-targeted treatment has led to an intense search for alternative predictive biomarkers. Oncogenic activation of signaling pathways downstream of the EGFR, such as mutation of KRAS, BRAF, or PIK3CA oncogenes, or inactivation of the PTEN tumor suppressor gene is central to the progression of colorectal cancer. Tumor KRAS mutations, which may be present in 35%-45% of patients with colorectal cancer, have emerged as an important predictive marker of resistance to panitumumab or cetuximab treatment. In addition, among colorectal tumors carrying wild-type KRAS, mutation of BRAF or PIK3CA or loss of PTEN expression may be associated with resistance to EGFR-targeted monoclonal antibody treatment, although these additional biomarkers require further validation before incorporation into clinical practice. Additional knowledge of the molecular basis for sensitivity or resistance to EGFR-targeted monoclonal antibodies will allow the development of new treatment algorithms to identify patients who are most likely to respond to treatment and could also provide rationale for combining therapies to overcome primary resistance. The use of KRAS mutations as a selection biomarker for anti-EGFR monoclonal antibody (eg, panitumumab or cetuximab) treatment is the first major step toward individualized treatment for patients with metastatic colorectal cancer.

Integration of panitumumab into the treatment of colorectal cancer

Conventional chemotherapy increases progression-free survival (PFS) and overall survival (OS) of metastatic colorectal cancer (mCRC) patients versus best supportive care (BSC). However, the efficacy of chemotherapy is limited. Recently approved monoclonal antibodies (MoAb) have a different mechanism of action, targeting growth factors or their receptors. Panitumumab is a fully human IgG2 MoAb directed against the epidermal growth factor receptor (EGFR). In phase II trials, panitumumab showed preliminary activity in chemorefractory mCRC. This efficacy was confirmed in a randomized pivotal phase III trial, which compared single-agent panitumumab plus BSC versus BSC alone. Several ongoing clinical trials are evaluating panitumumab in combination with different chemotherapy regimens in first- and second-line settings. Skin toxicities, hypomagnesemia, and diarrhea are the most common adverse events associated with anti-EGFR therapy. KRAS status and skin rash have been correlated with panitumumab efficacy. This article reviews the preclinical and pharmacokinetics data, activity and tolerance of panitumumab in mCRC patients. Potential predictive factors of response are also discussed.

Treatment of patients with colorectal cancer: emphasis on liver metastases

The treatment of colorectal liver metastases has progressed considerably in recent years. Coordinated multidisciplinary management of patients on clinical trials has resulted in 5-year survival rates exceeding 50%, and for certain patients cure is now a realistic goal. For all patients, the approval of six new drugs has contributed to an increase in median survival from 6 months to over 20 months. Recent molecular discoveries promise an era of tailored therapy in which only patients known to benefit will be treated, an approach that will enable more efficient use of the already stretched resources. Clinical trials continue to investigate different combinations and methods of administering approved therapies, but if the progress of the past decade is to be replicated it is imperative that we embrace innovative treatment strategies and novel trial designs. In this review, we highlight the developments that have improved survival for patients with colorectal liver metastases and discuss the many issues that challenge further progress.

The role of targeted therapy in the treatment of advanced colorectal cancer

The introduction of targeted therapies in the treatment of metastatic colorectal cancer (MCRC) has resulted in significant improvements in efficacy outcomes. Both vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) inhibitors have proven to be valid and valuable agents in the management of MCRC. This review will focus on the role of the anti-VEGF monoclonal antibody, bevacizumab, and the anti-EGFR monoclonal antibodies, cetuximab and panitumumab, in MCRC. Special focus will be placed on clinical evidence supporting the use of these agents in various lines of treatment, and on KRAS as a marker of response in relationship to anti-EGFR inhibitors.

A randomized phase IIIB trial of chemotherapy, bevacizumab, and panitumumab compared with chemotherapy and bevacizumab alone for metastatic colorectal cancer

PURPOSE

Panitumumab, a fully human antibody targeting the epidermal growth factor receptor, is active in patients with metastatic colorectal cancer (mCRC). This trial evaluated panitumumab added to bevacizumab and chemotherapy (oxaliplatin- and irinotecan-based) as first-line treatment for mCRC.

PATIENTS AND METHODS

Patients were randomly assigned within each chemotherapy cohort to bevacizumab and chemotherapy with or without panitumumab 6 mg/kg every 2 weeks. The primary end point was progression-free survival (PFS) within the oxaliplatin cohort. Tumor assessments were performed every 12 weeks and reviewed centrally.

RESULTS

A total of 823 and 230 patients were randomly assigned to the oxaliplatin and irinotecan cohorts, respectively. Panitumumab was discontinued after a planned interim analysis of 812 oxaliplatin patients showed worse efficacy in the panitumumab arm. In the final analysis, median PFS was 10.0 and 11.4 months for the panitumumab and control arms, respectively (HR, 1.27; 95% CI, 1.06 to 1.52); median survival was 19.4 months and 24.5 months for the panitumumab and control arms, respectively. Grade 3/4 adverse events in the oxaliplatin cohort (panitumumab v control) included skin toxicity (36% v 1%), diarrhea (24% v 13%), infections (19% v 10%), and pulmonary embolism (6% v 4%). Increased toxicity without evidence of improved efficacy was observed in the panitumumab arm of the irinotecan cohort. KRAS analyses showed adverse outcomes for the panitumumab arm in both wild-type and mutant groups.

CONCLUSION

The addition of panitumumab to bevacizumab and oxaliplatin- or irinotecan-based chemotherapy results in increased toxicity and decreased PFS. These combinations are not recommended for the treatment of mCRC in clinical practice.

Anti-EGFR monoclonal antibodies in metastatic colorectal cancer: time for an individualized approach?

Over the past 10 years, healthcare providers involved in the management of metastatic colorectal cancer (MCRC) have seen an explosion in new agents and their combinations. These developments have resulted in an expansion in the options of care for MCRC patients and in a significant improvement in their overall survival. This article reviews the current role of anti-EGFR monoclonal antibodies in the management of MCRC and the identification of recent markers of response that lead towards treatment individualization.