TYMS and colonic neoplasm: Attempts to identify chemotherapy predictive biomarkers of treatment response and resistance has yielded some results with high thymidylate synthase (TS) expression being a predictor of poorer outcome in 5-fu-based therapy and also 5-fu adjuvant treatment being ineffective in tumors with microsatellite instability[12–14];likewise higher levels of TOP1 is correlated with greater sensitivity of colon tumors to camptothecin derivatives compared with normal colonic mucosa, but there is no irinotecan predictive biomarkers that have reached a level of evidence allowing for routine clinical use[15].