The role of cetuximab in the treatment of squamous cell cancer of the head and neck.

The epidermal growth factor receptor (EGFR) is a member of the HER family of tyrosine kinase growth factor receptors. Binding to EGFR by its natural ligands, mainly epidermal growth factor (EGF) or transforming growth factor (TGF)-alpha, results in a conformational change in the receptor, which promotes homo- or heterodimerisation or oligomerisation with other EGFR molecules or other HER family members. Dimerisation results in the activation of intracellular tyrosine kinase, autophosphorylation and activation of signal transduction molecules, ultimately leading to cell cycle progression, reduced apoptotic capacity, angiogenesis and the metastatic phenotype. EGFR is expressed on normal human cells and also across a range of malignancies. Tumour EGFR expression correlates with poor prognosis and resistance to therapy. Cetuximab is a chimeric human:murine monoclonal antibody that binds competitively to the EGFR. Binding of the antibody to the EGFR prevents activation of the receptor by endogenous ligands; proliferation is reduced, apoptosis enhanced, and angiogenesis, invasiveness and metastasis reduced. Binding of cetuximab to the receptor also results in internalisation and degradation of the antibody-receptor complex, downregulating EGFR expression. EGFR has been recognised as an important therapeutic target in cancer. Other antibodies are also in development, and small molecular inhibitors of the tyrosine kinase domain are available. Cetuximab adds to the activity of radiotherapy in locoregional head and neck cancer, and when given with platinum-based chemotherapy is active in a proportion of patients with platinum-refractory recurrent or metastatic squamous cell carcinoma of the head and neck, as is cetuximab monotherapy. When cetuximab is added to cisplatin monotherapy in the first-line treatment of recurrent or metastatic squamous cell carcinoma of the head and neck, the objective response rate is significantly improved and the hazard ratio for progression is 0.78. The most commonly reported adverse event associated with cetuximab treatment is an acneiform rash that occurred in 70 - 80% of patients treated with cetuximab. Presence of the characteristic rash is significantly associated with response and/or survival. It is possible that development of acneiform rash may become an important clinical prognostic marker. Serious cetuximab-related toxicities include hypersensitivity reactions. Thus, cetuximab is biologically active across a range of clinical scenarios in squamous cell carcinoma of the head and neck. Ongoing studies will be important in establishing its role in the routine management of head and neck cancer.