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Introduction: Patients with oral leukoplakia and other oral potentially malignant disorders (OPMD) have an increased risk for oral cancer development. Extensive research efforts are currently directed toward identification of agents which can prevent or delay progression to invasive carcinoma in these high risk patients. Although cancer development is the ideal endpoint to monitor for efficacy, years may elapse before malignant progression. Many clinical trials therefore utilize surrogate endpoints such as clinical appearance or pathologic grade of dysplasia to assess response to study agents. The subjective nature of clinical examination and potential for sampling error with small biopsy samples may limit the ability of oral chemoprevention trials to accurately evaluate the potential efficacy of study agents in patients with OPMD based on clinical examination and/or pathologic evaluation of biopsy samples. The purpose of this study is to evaluate the feasibility of using noninvasive optical imaging approaches for quantitative comparisons of oral lesions in patients participating in an oral cancer chemoprevention trial. Material and Methods: Twenty-three patients with visible oral lesions enrolled on the Erlotinib Prevention of Oral Cancer chemoprevention trial (EPOC) were simultaneously enrolled in diagnostic optical imaging and spectroscopy trials. EPOC is a multicenter trial to test the ability of an epidermal growth factor receptor (EGFR) inhibitor to reduce the incidence of oral cancer in high-risk patients. These 23 patients are also being followed over time with standard clinical examination, autofluorescence imaging (AFI), and optical spectroscopy. The AFI device captures autofluorescence images of a 4-5 cm diameter region of oral mucosa using an excitation wavelength of 405 nm, optical filters, and a camera. The spectroscopy device collects autofluorescence and reflectance spectra from selected sites using a 4 mm diameter fiber optic probe. Normalized red:green fluorescence intensity ratios from AFI and posterior probability risk scores generated by an algorithm from spectroscopy exams are recorded. Objective optical data from successive exams over time are compared to clinical exam and pathologic results from any corresponding biopsies. Results: During the 30-month period from February 2010 to August 2012 a total of 89 in vivo measurement sessions were carried out, producing data from 64 unique oral sites in 23 subjects. Of the 64 sites tracked, there were 45 corresponding histopathologic diagnoses available at some point during the study period. To date, 18 of the patients have been measured over the course of three or more visits. Conclusion: Results illustrate a potential for objective optical diagnostic evaluations to assist in monitoring response to test agents during oral chemoprevention trials. Citation Format: Jana M. Howe, Sharon Mondrik, Richard Schwarz, Tim Quang, Vijayashree Bhattar, Sohini Dhar, Mary K. Quinn, William William, Jr., Michelle D. Williams, Rebecca Richards-Kortum, Ann M. Gillenwater. Assessment of quantitative optical measurements of mucosal lesions as a surrogate biomarker in patients participating in an oral cancer chemoprevention trial. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B109.