Archival paraffin blocks frequently are studied to evaluate the expression of biomarkers in tumors and disease states. The identification of biomarkers is becoming increasingly important to identify and characterize early preinvasive neoplastic lesions (1 –3 ), and to correlate the expression of specific biomarkers with diagnosis and prognosis of invasive tumors (4 –6 ). Also, the expression of biomarkers in archival tissues is sometimes used to identify patients who may be eligible for novel therapies, including gene therapy and immunotherapy, as well as to monitor the effectiveness of conventional and novel therapies using changes in the expression of biomarkers as surrogate endpoints (7 –12 ). In addition, the response of some tumors to specific therapies has been correlated with specific biomarker expression (13 ).