Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Epidermal growth factor receptor (EGFR) inhibitor-induced rash: a consecutive patient series that illustrates the need for rigorous palliative trials

PURPOSE

Rash is the most common side effect of epidermal growth factor receptor (EGFR) inhibitors and negatively impacts quality of life. This single-institution study sought to explore how rash is currently managed outside a clinical trial setting and to further characterize general clinical aspects of this rash.

METHODS/RESULTS

Among 4101 consecutive patients with cancer of the lung, colorectum, pancreas, and head and neck, 138 had received an EGFR inhibitor. Within this group, 96 (69%) developed a rash. Forty-nine of these patients were prescribed rash therapy, and a total of 26 different palliative regimens were used. Surprisingly, most patients, with the exception of 2, appear to have manifested evidence of rash improvement-even when unproven or disproved therapies had been prescribed. Fourteen patients stopped their EGFR inhibitor because of rash, and 11 were then able to restart. No demographic variables were able to predict rash development.

CONCLUSION

The observation that multiple, largely unproven, anecdotal therapies are being prescribed to palliate EGFR inhibitor-induced rashes underscores the need for more rigorous, prospective palliative trials.

Interdisciplinary management of EGFR-inhibitor-induced skin reactions: a German expert opinion

BACKGROUND

Anti-epidermal growth factor receptor treatment strategies, i.e. monoclonal antibodies such as cetuximab and panitumumab, or epidermal growth factor receptor (EGFR) small molecule tyrosine kinase inhibitors, such as erlotinib and gefitinib, have expanded the treatment options for different tumor types. Dermatologic toxic effects are the most common side-effects of EGFR inhibitor therapy. They can profoundly affect the patient's quality of life.

PURPOSE

The aim of this study was to provide interdisciplinary expert recommendations on how to treat patients with skin reactions undergoing anti-EGFR treatment.

MATERIAL AND METHODS

An expert panel from Germany with expertise in medical oncology, dermatology or clinical pharmacology was convened to develop expert recommendations based on published peer-reviewed literature.

RESULTS

The expert recommendations for the state-of-the-art treatment of skin reactions induced by EGFR inhibitor therapy include recommendations for diagnostics and grading as well as grade-specific and stage-adapted treatment approaches and preventive measures. It was concluded that EGFR-inhibitor-related dermatologic reactions should always be treated combining basic care of the skin and a specific therapy adapted to stage and grade of skin reaction. For grade 2 and above, specific treatment recommendations for early- and later-stage skin reactions induced by EGFR-inhibitor therapy were proposed.

CONCLUSION

This paper presents a German national expert opinion for the treatment of skin reactions in patients receiving EGFR inhibitor therapy.

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.