Frequency of gefitinib responder mutations in EGFR (+) squamous cell carcinoma of the head and neck

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Gefitinib is a small molecule tyrosine kinase inhibitor with activity against the epidermal growth factor receptor (EGFR). EGFR is highly expressed in squamous cell carcinomas of the head and neck (H&N SCC). A recent phase II study reported a 10.6% response rate and a 53% disease control rate using gefitinib as monotherapy in these tumors. In earlier studies this year, mutations in EGFR exons 19 and 21 were found to be associated with a dramatic clinical response to gefitinib in EGFR expressing non-small cell lung tumors. It was postulated these mutations alter the kinase domain, thereby stabilizing the interaction between certain amino acid residues and gefitinib. The presence or absence of mutations in these exons and their frequency in H&N SCC has not been reported. Determining the status and frequency of mutations in these exons may help to rationally stratify the administration of gefitinib to potential responders. Eleven cases of H&N SCC were identified from the archival files of the Roswell Park Cancer Institute. All cases were stained with a monoclonal antibody to EGFR (Dako, Carpenteria, CA). An additional slide was cut, deparaffinized, stained with hematoxylin and dehydrated. EGFR expressing tumor cells were identified from the immunohistohemically stained slide and procured from the unstained slide using a PixCell II laser capture instrument (Arcturus, MountainView, CA). The procured cells were digested with proteinase K and the DNA isolated using spin columns (Zymo Research, Tustin, CA). Primers specific for EGFR exons 19 and 21 were used for polymerase chain reactions (PCR). The amplified product was excised from an agarose gel and isolated using spin columns (Qiagen, Valencia, CA). The PCR product was sequenced on an ABI Prism 3100 using BigDye Ternminator kit v3.1. Exons 19 and 21 could be amplified from the available DNA in eight of eleven cases (8/11). The remainder of cases had no amplification for either exons. A paired sequence analysis of the exons from each sample with the wild type sequence showed no evidence of mutations in either exon. These results show that clinical material fixed in formalin and paraffin embedded can retrospectively be analyzed at the molecular level for potential targeted therapy. It also emphasizes the need to include molecular analysis in the treatment assessment of patients being considered for targeted molecular agents. Based on the absence of “responder mutations” in EGFR exons 19 and 21 in this study, H&N SCC may not be an appropriate candidate for gefinitib. Additional cases will need to be studied. Alternative explanations for the clinical success of gefitinib in EGFR (+) H&N SCC trials may need to be investigated.