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3511 Background: Radiotherapy reduces local recurrence (LR) when combined with surgery in resectable rectal cancer. The Medical Research Council CR07 trial was designed to compare two different radiotherapy policies when combined with mesorectal excision. Methods: Patients with operable non-metastatic adenocarcinoma of the rectum were randomised to either routine pre-op short course radiotherapy [25Gy/5F] (PRE) or selective post-op chemoradiotherapy (POST) for patients with involvement of the circumferential resection margin (CRM) - [45Gy/25F + 5fluorouracil]. Results: A total of 1350 patients were randomised from 52 centres in the UK, Canada, New Zealand and South Africa between March 1998 and August 2005. Median follow-up is 3 years. Patients (73% male, median age 65 years, 79% PS0) were well balanced between the 2 arms. 595 of 674 (88%) of the pre-op group received their allocated treatment. Of the 676 patients allocated to the selective post-op chemoradiotherapy arm, 73 (11%) were CRM +ve and 51 of these (70%) received chemoradiotherapy. Post operative chemotherapy was received by 85% of patients with stage III disease. At the time of analysis 23 PRE and 61 POST patients had confirmed LR, 96 and 106 patients respectively distant metastases, and 115 and 146 respectively had died. The 3 year rates for LR (primary end point) were 4.7% and 11.1% for PRE and POST groups respectively (HR 2.47, 95% CI 1.61–3.79), for disease free survival 79.5% and 74.9% (HR 1.31, 95% CI 1.02–1.67) and for overall survival 80.8% and 78.7% (HR 1.25, 95% CI 0.98–1.59. The LR benefit in favour of PRE was consistent for tumours 0–5,5–10 and >10cm from the anal verge (HR 2.00, 2.14 and 4.97 respectively). Further subset analysis based on TNM stage and operation performed will be presented. Conclusions: These preliminary results indicate that routine short course pre-operative radiotherapy results in a signifcant reduction in local recurrence and improved disease free survival at 3 years when compared with a highly selective post operative approach. No significant financial relationships to disclose.

3512 Background: The MRC CR07 trial compared routine short course pre-operative radiotherapy (PRE) with selective post-operative chemo-radiation if there was involvement of the circumferential resection margin (CRM) (POST) and included a prospective pathological assessment of the quality of resection of the surgical specimen. Methods: A total of 1350 patients were randomised from 52 centres between March 1998 and August 2005. Median follow-up is 3 years. Trial pathologists were trained in histopathological assessment and reporting of the involvement of the CRM and plane of surgery (PoS) according to pre-set criteria describing the plane of dissection (Grade 1-muscularis plane: 2-intramesorectal plane: 3-mesorectal plane). 1232 patients were prospectively assessed for CRM and 1119 for PoS. Results: The CRM was involved (tumour ≤1mm) in 139 (11%) of resected specimens, and for these patients the 3-year local recurrence (LR), disease-free survival (DFS) and overall survival rates were 18%, 50% and 57%. For the 1093 patients with CRM-ve the respective rates were 7%, 81% and 84%. LR and DFS rates were associated with PoS (log-rank test p=0.0019 and p=0.0506 respectively), and in addition there was clear evidence of a reduction in LR and improvement in DFS rates in favour of PRE for all grades of quality of surgical assessment as shown in the table . Conclusions: The results indicate a strong association between the quality of surgery and the rates of local recurrence and disease-free survival, as well as a clear benefit from the addition of PRE to all grades of surgical dissection. Thus for patients with rectal cancer short-course pre-operative radiotherapy and good quality surgery can almost completely eliminate local recurrence. [Table: see text] No significant financial relationships to disclose.

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