LAUSR

413 Background: Treatment of high grade non-muscle invasive bladder cancer (HG NMIBC) is controversial with BCG instillation and early cystectomy as viable options. However, accurate predictive markers for HG NMIBC are lacking. Refractive index (RI) is an optical feature of tissues and has been shown to be correlated with various oncologic outcomes in prostate and breast cancers. The role of RI in NMIBC has not been explored yet. The aim of this study is to measure and compare RI values of benign and malignant low and high grade NMIBC. Methods: After IRB approval, tissue samples were obtained from high and low grade NMIBC patients. Measurements were performed on non-stained slides using digital holography. Areas of benign and malignant tissues were marked by a fellowship trained GU pathologist. The average RI (RIavg) and RI variance (RIvar) over malignant and benign cell nuclei were measured. Comparison between benign and malignant tissue and between low and high grade tumors was performed with the Student's t-test. Results: Multiple nuclei of LG and HG patients were measured . Mean difference of RIavg between malignant and benign cells was 0.03 in HG patients (p < 0.001). Mean difference of RIvar between malignant and benign tissues was 0.016 in HG patients (p < 0.001). In LG tissues, there was no significant difference in RIavg or RIvar between benign and malignant cells. Finally, there was a significant difference in RIavg between HG and LG cells (p < 0.001). Conclusions: For the first time, RI was measured in bladder cancer tissue by digital holography. The RI values and variance were different between malignant and benign cells in HG tissues. Furtheremore, we found a significant difference in RI values between HG and LG cells. This technology may assist in the future in tissue diagnosis and classification of bladder tumor.