Background: Patients with advanced colorectal cancer with 4WT tumors achieve increased response rates with chemotherapy and anti-EGFR therapy as compared with chemotherapy alone. In clinically staged (c) T3 rectal cancer neoadjuvant oxaliplatin/fluoropyrimidine combination has shown to induce encouraging pathological complete response (pCR). We hypothesize that combining FOLFOX and P could improve outcomes in 4WT tumors. Methods: PIER was an investigator-initiated phase II, single-arm, multicentre clinical trial to evaluate the safety and efficacy of neoadjuvant mFOLFOX6 with P in pts < 75-y, with 4WT rectal cancer of the middle third staged as T3 by centrally-reviewed magnetic resonance imaging (MRI) and clear MRF, who were candidate for a R0 resection with sphincter preservation surgery. Pts received 6 cycles and underwent re-staging with MRI and sigmoidoscopy. Pts without progression underwent total mesorectal excision 4 weeks after the last cycle. Patients with progression were treated with pre-op chemoradiotherapy. The primary endpoint was pCR. The study followed a 2-Stage Simon’s MiniMax design (P0 of 16%, P1 of 35%, alpha and beta of 0.1). The target sample size was 35 patients and if 9 or more achieved a pCR, the results would be compatible with efficacy. We present primary and early secondary endpoints. Results: Between 9/2017 and 6/2020, 90 patients were screened (56 excluded; 42 were excluded due to mutations, 12 were excluded due to discrepancies with central review of radiology) of whom 34 were enrolled. In the ITT population a pCR was observed in 11 pts (32.3%; [95% CI 17.39-50.53]) and a near-complete pathological response (Mandard 1+2) was observed 17 pts (52.9%). Clinical complete or near complete response was achieved in 50% and there were no progressions. R0 resection rate and pathological circumferential resection margin neg- were 100%. Full compliance with induction was 88%. Neoadjuvant G3/4 toxicity occurred in 54% and was consistent with FOLFOX/P safety profile. G3/4 postoperative related toxicity was 19% with one reoperation. Conclusions: The study met the threshold for efficacy. mFOLFOX6 with P as neoadjuvant therapy can be effective and safe without unexpected toxicities in mrT3, clear MRF and 4WT rectal cancer and resulted in a higher rate of pCR compared with our previous series (GEMCAD 0801; The Oncologist 2014) in a similar molecular-unselected population. This study was funded by Amgen S.A. Clinical trial information: NCT03000374