The Efficacy of topo i -pS10 Expression in Gastric Cancer as a Predictive Biomarker for Irinotecan Use

Background: Though irinotecan is commonly used for treating advanced gastric cancer, there is no predictive biomarker to date. We have studied the resistant mechanism for irinotecan and found that phosphorylation of serine 10 residue of topoisomerase I (topo I) is an important step for irinotecan resistance. We have developed an immunohistochemical staining-based biomarker: topo I -pS10, for predicting irinotecan efficacy. Purpose: The purpose of this study is to test the accuracy of topo I -pS10 immunohistochemical staining in gastric cancer clinical samples. Methods: In this study we performed 2 sets of tests. In the training set, we stained 79 gastric cancer clinical samples which efficacy of irinotecan was measured by succinate dehydrogenase inhibition (SDl)test. In the validation set, we used 27 gastric cancer clinical samples which irinotecan was used and the efficacy was known. Results: Training set: From the ROC curve the cut-off point was set at 35% positive nuclei. Sixty three cases were positive with topo I -pS10 in the nuclei. With the result of irinotecan SDI, the sensitivity was 76.6% and the positive predictive value was 92.5%. This result showed that topo I -pS10 positive case does not respond to irinotecan. Validation set: In this set, the sensitivity was 82.4% and the positive predictive value was 82.4%. Conclusion: topo I -pS10 staining can be used as a predictive biomarker for irinotecan for gastric cancer patients.