Epidermal growth factor receptor expression in invasive thymoma

Purpose: Epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein with intrinsic tyrosine kinase activity. Activation results in a variety of cellular responses including cell proliferation and differentiation. In clinical trials, anti-EGFR is showing promise in the treatment of solid tumors expressing EGFR. Thus, we assessed EGFR expression in a series of thymic epithelial tumors. Methods: Tumors from 37 patients seen at Indiana University School of Medicine (IUMC) for treatment of thymoma (31 patients) or thymic carcinoma (six patients) were assessed for EGFR expression. Five-micron sections of formalin-fixed, paraffin-embedded tumor (28 invasive and/or metastatic thymomas, six thymic carcinomas, and three non-invasive thymomas) were stained with anti-EGFR. Any degree of cytoplasmic membrane staining of tumor cells was considered positive; furthermore, staining was scored 0 to 3 + using criteria as standardized for HER-2/neu assessment of breast carcinoma. Appropriate controls were performed. Results: Positive staining of tumor was observed in 28 tumors {23 invasive and, or metastatic thymomas, two thymic carcinomas, and three non-invasive thymomas). Conclusions: EGFR is expressed in a high percentage of thymic epithelial tumors. EGFR is often strongly expressed and is a potential therapeutic target in patients with malignant thymic tumors. We are pursuing additional studies to assess anti-EGRF in the treatment of patients with advanced thymoma.