Background: The PETACC-6 trial investigates whether the addition of oxaliplatin to preoperative oral fluoropyrimidine-based chemoradiation (CRT) followed by postoperative adjuvant fluoropyrimidine-based chemotherapy (CT) improves disease-free survival (DFS) in locally advanced rectal cancer. We present results of the early secondary endpoints. Methods: Between 11/2008 and 09/2011, patients with rectal cancer within 12 cm from the anal verge, T3/4 and/or node-positive, with no evidence of metastatic disease and considered either resectable at the time of entry or expected to become resectable after preoperative CRT, were randomly assigned to receive 5 weeks of preoperative CRT (45 Gy in 25 fractions) with capecitabine (825 mg/m² twice daily), followed by 6 cycles of adjuvant CT with capecitabine (1000 mg/m²twice daily/days 1-15 every three weeks) (arm 1) or to receive the same regimen with the addition of oxaliplatin before (50 mg/m²/days 1, 8, 15, 22, 29) and after surgery (130 mg/m²/day 1, every three weeks) (arm 2). Additional RT before surgery (5.4 Gy/days 36-38) using the same fields or as a boost with capecitabine was an option. Primary endpoint is DFS. Results: 1094 patients were randomized (547 in each arm). 98% and 92% of patients, respectively, received at least 45 Gy of preoperative RT in arm 1 and arm 2. More than 90% of full dose concurrent CT was delivered in 91% and 63% of patients, respectively, in arm 1 and arm 2. Preoperative grade 3/4 toxicity occurred in 15.1% of patients in arm 1 vs. 36.7% in arm 2; 1 vs. 3 patients died before surgery. R0 resection rate was 92.0% in arm 1 and 86.3% in arm 2. The pCR rate (ypT0N0) was equal in both arms with 11.3% in arm 1 and 13.3% in arm 2 (p=0.31). The anal sphincter was preserved in 70% vs. 65% (p=0.09) in arm 1 and 2. Postoperative complications were not different between arms (38% vs. 41%; 5 vs. 4 patients died following surgery). Definitive numbers will be presented at the congress. Conclusions: The addition of oxaliplatin to preoperative fluoropyrimidine-based CRT led to decreased treatment compliance and increased toxicity, but did not improve surgical outcome. Clinical trial information: NCT00766155.