Molecular Markers of Radiation Effectiveness in Head and Neck Squamous Cell Carcinoma

The response of cancer to ionizing radiation treatment varies in a manner not fully explained by standard clinical, demographic, or histologic factors. Response may be related to intrinsic biologic capability of the tumor cells and/or the host immune or stromal support tissues. The availability of molecular biological methods to detect specific tumor-related genetic alterations and altered protein expression has prompted a search for molecular markers that accurately predict tumor response to therapy. Tumor suppressor genes and oncogenes such as p53 and Cyclin D1, key components of pathways that control tumor behavior, such as epidermal growth factor receptor and apoptotic factors including bcl-2, markers of proliferation (Ki-67), and markers of angiogenesis such as vascular endothelial growth factor have been examined. To date, results for each of these are mixed. This is not surprising given the complexity of the biologic system of tumor response to damage and the multitude of factors that contribute to the diversity of clinical presentation of disease. This manuscript reviews the literature to date in an effort to summarize results and suggest the direction for further study.