Background: We recently determined that overexpression of epidermal growth factor receptor (EGFR) together with human papillomavirus (HPV) negative status in pretreatment biopsies is an indicator of poor survival in advanced oropharyngeal cancer patients. HPV16 presence and copy number in the biopsy is associated with good response to induction chemotherapy, good response to concurrent chemotherapy and radiation, and with good overall and disease specific survival (DSS). HPV copy number is also associated with elevated proliferating cell nuclear antigen (PCNA) expression. We postulated that high PCNA expression might be a marker of chemotherapy response and or outcome. Methods: Pretreatment biopsies from advanced oropharyngeal cancer patients enrolled in a clinical trial at the University of Michigan were analyzed for the expression of PCNA, tumor HPV status and EGFR expression. The impact of the combined expression of these biomarkers on survival of the patients was assessed. Results: Patients with HPV positive tumors had significantly higher tumor expression of PCNA (p=0.033). Similarly, PCNA and HPV were inversely associated with current, past and never smoking status (HPV p=0.04; PCNA p=0.04) and both were directly associated with wild type p53 status (HPV p=0.01; PCNA p=0.04). In contrast to HPV, PCNA as a single marker was not associated with either response to induction chemotherapy (p=0.6) or response to chemo/RT (p=0.6). Furthermore, expression of EGFR and PCNA were strongly correlated (p=0.03). However, when the interaction of EGFR and PCNA expression was examined, patients with tumors expressing high EGFR/low PCNA had the worst DSS whereas patients with low EGFR/high PCNA had the best DSS. Patients with high EGFR and high PCNA had intermediate DSS suggesting that high PCNA has a moderating effect on EGFR. Patients with low EGFR and low PCNA had high probability of increased DSS although three patients in this group died of late distant metastasis. Conclusions: High EGFR expression in pretreatment biopsies is associated with poor outcome in advanced oropharynx cancer. However, the adverse effect of EGFR on survival is partially modified by the presence of high HPV. Similarly, high expression of PCNA is associated with the presence of HPV, and like HPV, PCNA expression also appears to have a modifying effect on outcome in tumors with high EGFR expression. The mechanisms that determine response to therapy and survival in oropharynx cancer remain complex, but investigation of pretreatment biomarker expression and their interactions is beginning to define outcome cohorts that will help to identify those patients in need of additional therapy.
Second AACR International Conference on Molecular Diagnostics in Cancer Therapeutic Development-- Sep 17-20, 2007; Atlanta, GA