EGFR expression in invasive anal carcinoma.
412 Background: Squamous cell anal carcinoma (SCAC) treatment remains unchanged since the institution of chemoradiation over 4 decades ago. Epidermal growth factor receptor (EGFR) is a protein often expressed in aggressive cancers and that is the target of the monoclonal antibody: cetuximab. Concurrent cetuximab and radiation has been particularly effective treating squamous cell carcinoma of the head and neck. Like head and neck cancer, anal cancer is an epithelial tumor of the alimentary tract that is radioresponsive and is associated with HPV infection. The rarity of this cancer limits its evaluation for biological markers. This study set out to thoroughly characterize EGFR expression by immunohistochemistry in 101 invasive SCAC tissue samples. Methods: One hundred and one pretreatment paraffin embedded invasive SCAC biopsies, obtained from the Montreal area between 1999 and 2009, were tested for EGFR expression by immunohistochemistry. All samples were confirmed to harbor invasive anal carcinoma on H&E slide preparations. Corresponding cancerous areas were identified on paraffin tissue blocks and cut out for tissue microarray analysis. Samples were immunostained with an EGFR antibody (clone SPM 341) on the Discovery XT Autostainer (Ventana), and staining was assessed by light microscopy by two pathologists. A semiquantitative combination score combining staining intensity with the percent of cells staining gave a final score: just detectable or weak (1+); moderate (2+); strong/intense (3+). Results: Of 101 patient biopsies, 82 samples had sufficient material for interpretation. Of these samples, 72/82 (90%) stained positive for EGFR, while 41/82 (50%) samples displayed at least moderate to strong staining. Conclusions: This is the largest cohort of SCAC tissue samples tested to date for EGFR expression and it confirms that the vast majority of invasive SCAC overexpress EGFR. EGFR likely plays a role in anal cancer tumor-genesis and progression. Testing of EGFR inhibitors in this patient population is justified. No significant financial relationships to disclose.