Anti-EGFR therapies: clinical experience in colorectal, lung, and head and neck cancers.

Anti-EGFR (epidermal growth factor receptor) therapies, including tyrosine kinase inhibitors (TKIs) and monoclonal antibodies, demonstrate activity in a variety of tumor types. While both inhibit the EGFR pathway, they act via different mechanisms. Monoclonal antibodies bind to the extracellular domain of EGFR, preventing ligand binding and interrupting the signaling cascade. Tyrosine kinase inhibitors bind to the intracellular domain of EGFR and inhibit the downstream effects of EGFR ligand binding. Both categories of agents have been evaluated in a variety of clinical settings and tumor types, including colorectal cancer, non-small-cell lung cancer (NSCLC), and squamous cell carcinoma of the head and neck (SCCHN). Phase II/III trials in patients with previously treated or untreated metastatic colorectal cancer, including those with documented refractory disease, demonstrate activity of the monoclonal antibody cetuximab (Erbitux) as a single agent or in combination with both irinotecan (Camptosar)- and oxaliplatin (Eloxatin)-based chemotherapy. Activity of cetuximab added to chemotherapy in patients who previously progressed on the same regimen suggests an ability to overcome chemotherapy resistance in some patients. In NSCLC, phase II trials of the TKI gefitinib (Iressa) plus combination chemotherapy showed impressive activity with considerable toxicity. Large, randomized, phase II trials (IDEAL 1 and 2) reported modest activity of gefitinib in NSCLC; however, phase III trials (INTACT 1 and 2)failed to demonstrate a benefit to adding gefitinib to chemotherapy. A similar trend was noted in trials of erlotinib (Tarceva) (TALENT and TRIBUTE). Phase II/III trials have shown promising activity of cetuximab in SCCHN, generating significantly improved survival in combination with radiotherapy over radiotherapy alone in locally advanced disease and significantly improved response rates in combination with chemotherapy over chemotherapy alone in recurrent/metastatic disease, with little enhancement of toxicity profiles. Limited clinical experience with TKIs in SCCHN suggests similar degrees of single-agent activity and dermatologic toxicities. Levels of EGFR expression and the presence of EGFR mutations correlate with responsiveness to TKI therapy, while it remains unclear whether a relationship exists between level of EGFR expression and cetuximab efficacy in colorectal cancer. Anti-EGFR therapies are good candidates for combination with other treatment modalities, including chemotherapy and radiotherapy, due to their tolerable safety profile and nonoverlapping toxicities. In addition, these agents represent important treatment options in patients ineligible for chemotherapy due to refractory or resistant disease. Ongoing trials continue to investigate both the monoclonal antibodies and TKIs in various treatment settings.