AIM To clarify which factors may influence pathological tumor response and affect clinical outcomes in patients with locally advanced rectal carcinoma treated with neo-adjuvant chemoradiotherapy and surgery.METHODS Tumor regression grade(TRG) according to the Dworak system and yT NM stage were assessed and correlated with pre-treatment clinico-pathological variables in 215 clinically locally advanced(c TNM stage Ⅱ and Ⅲ) rectal carcinomas. Prognostic value of all pathological and clinical factors on disease free survival(DFS) and cancer specific survival(CSS) was analyzed by Kaplan Meier and Cox-regression analyses.RESULTS cN + status, mucinous histotype or poor differentiation in the pre-treatment biopsy were significantly associated with lower pathological response(low Dworak grade and TNM remaining unchanged/upstaging). Cases showing acellular mucin pools in surgical specimens all had unremarkable clinical courses with no deaths or recurrences during follow-up. Dworak grade had prognostic significance for DFS and CSS. However, compared to the 5-tiered system, a simplified twotiered grading system, in which grades 0, 1 and 2 were grouped as absent/partial regression and grades 3 and 4 were grouped as total/subtotal regression, was more reproducible and prognostically informative. The twotiered Dworak system, yN stage, craniocaudal extension of the tumor and radial margin status were significant independent prognostic variables. CONCLUSION Our data suggest that caution should be applied in using a conservative approach in rectal carcinomas with c N+ status, extensive/lower involvement of the rectum and mucinous histotype or poor differentiation. Although Dworak TRG is prognostically significant, a simplified two-tiered system could be preferable. Finally, cases with acellular mucin pools should be carefully evaluated to definitely exclude residual mucinous carcinoma.