739 Background: Several systems describe tumour regression grade (TRG) after neo-adjuvant chemo-radiotherapy (nCRT) in rectal cancer; however, there is lack of literature on factors predicting TRG and its prognostic significance when comparing two TRG systems. Methods: Chart review of 187 patients (pts) diagnosed with rectal cancer managed at our institution identified clinical T3 or T4 and/ or node positive adenocarcinoma who completed nCRT between 2005-2011. Assessment of TRG post-nCRT in 104 pts was determined using College of American Pathologists (CAP) and Modified Rectal Cancer Regression Grade (mRCRG) scoring systems. Logistic regression model was used to identify factors associated with TRG. Overall survival (OS) was estimated using Kaplan-Meier method, log-rank test to compare groups and Cox proportional hazard model to estimate hazard ratio. Results: Median age of 103 eligible pts was 64 (range [r] 31-88) and 70% were male. Median pre-nCRT tumour size was 4 cm (r 0.5-12). 61% tumours were distal. Radiation dose (RD) was >54 Gy in 57%, 50.4 Gy in 40%, and 45 Gy in 3% patients. 71% received concomitant 5 FU; 12% capecitabine and 17% according to clinical trials prior to radical surgery. Median time between completion of nCRT and surgery was 49 days. CAP scoring was 0 (21%), 1 (7%), 2 (19%), and 3 (53%) whereas mRCRG scoring was 1 (31%), 2 (21%), and 3 (48%). With median follow up 5.04 years (yr), 5 yr OS was 65%. OS was 77% for CAP 0 and 1 vs. 59% for CAP 2 and 3 (p=0.0483, HR2.4); mRCRG 1 and 2 OS was 75% vs 54% for mRCRG 3 (p= 0.0060, HR2.6). >30% reduction in pre-nCRT tumour occurred in 63% of CAP 1, 2, and 3 cases. Age (≥65 yr), higher RD and higher pre-op CEA were associated with mRCRG grade 3 (p=0.0339, 0.0415, and 0.0760 respectively). Tumour size, location, grade, type of chemotherapy, or gender were not predictive of TRG. Conclusions: Favorable TRG post-nCRT is associated with a statistically significant OS advantage. Younger age and RD escalation are associated with favorable TRG. CAP and mRCRG scoring systems of TRG were comparable for prognosis. nCRT leads to a significant cytoreduction in 63% of non-complete responders. TRG may have a future role in decisions on surgery, organ sparing, adjuvant chemotherapy, surveillance and patient counseling.
PTU-053 Prognostic significance of tumour regression grade in rectal carcinoma – a 5 year study