Is there any significant difference between tumor regression grade systems of rectal cancer?

3583 Background: Tumor regression grade (TRG) is a measure of histopathologic response of rectal cancer to preoperative chemoradiation (CRT) and correlates with outcomes. Several TRG systems have been reported including Mandard (5, 3 tier), Dowrak/Rodel (5, 3 tier), Memorial Sloan Kettering Cancer Center (MSKCC), and American Joint Committee of Cancer (AJCC). The purpose of this study is to compare the different TRG systems and determine which one(s) best predict recurrence and survival. Methods: Review of prospective maintained database from 1998 to 2007 identified 563 patients with locally advanced rectal cancer (T3/4 and/or N1) and treated with long-course CRT followed by total mesorectal excision. TRG was determined by measuring proportion of tumor mass replaced by fibrosis. Patients were then classified into the various TRG schemes which were compared by analyzing association with recurrence and survival using concordance index (CI) and reclassification index. CI is a measure that summarizes the predictive strength of a marker. Computing and contrasting CI across several markers is a way of selecting the best prognostic marker. Results: 75% of patients were noted to have clinical stage III disease by endorectal ultrasound or rectal MRI. Following resection with median follow-up of 39.3 months, 2% developed local recurrence and 17% developed distant metastasis. The median interval time between completion of CRT and surgery is 48 days. 20% demonstarted complete pathological response. CI of the 3 tier Mandard, 3 tier Dowrak/Rodel, MSKCC and AJCC are 0.665, 0.653, 0.683, and 0.694, respectively (higher number indicates better prediction). The AJCC was significantly more accurate in predicting recurrence than the 3- tier Mandard (p=0.002), and Dowrak/Rodel (p=0.006). AJCC had a higher CI than MSKCC although it did not reach significance (p=0.068). Comparing the 3 tier systems, MSKCC was most accurate and correctly reclassified 17 % and 23 % of the patients Mandard and Dowrak/Rodel systems, respectively. Conclusions: TRG predicts recurrence and survival following combined modality therapy for rectal cancer. The TRG system that recently was proposed in the 7thAJCC staging is currently the most accurate predictor.