Background: Rectal carcinomas are one of ten leading causes of death in India. There is gradual rise in their incidence which has prompted the greater research into their behavior. Now world wide all locally advanced rectal carcinomas are treated with preoperative chemo or radiotherapy. Aims and objectives: To observe the post chemotherapy histopathological changes in pretreated rectal carcinoma. Material and Methods: the present was both prospective and retrospective study conducted at Department of Pathology, on the 36 cases who had received pre-operatives NACT (Neoadjuvant chemotherapy). Results: Out of these 36 cases none showed complete remission of tumor. Both cytoplasmic and nuclear changes were observed and documented. The most common findings was cytoplasmic eosinophilia (98% of cases) and stromal dense fibrosis was seen in TRG3 tumors. The residual tumors were classified as TRG 0,1,2,3 as according to Dworak, Rodel and AJCC TNM system. The Rodel system was better as it was more objective and reducing the subjective bias in resected specimens. Conclusion -Hence the pathologist awareness towards the assessment of therapeutic response including the evaluation of residual tumor burden or tumor response grading (TRG) and cytomorphology including the stromal changes has become the hour of need.

Keywords: Rectal Carcinoma; Neoadjuvant Chemotherapy; Post Chemotherapy Changes; Tumor Regression Grading (TRG).