P-314Do we need adjuvant therapy in patients with rectal cancer and pathologic complete response, after conventional preoperative chemoradiation and laparoscopic (LapTME) or Transanal total mesorectal excision (TaTME)?

Introduction: The benefit of adjuvant chemotherapy for patients with rectal cancer and pathological complete response (pCR) after preoperative chemoradiation (CRT) and surgery, is controversial. We evaluated long-term oncological outcomes, in two prospective cohorts of rectal cancer patients treated in our Institution. Methods: All patients received neoadjuvant chemotherapy (fluorouracil 225mg/m2/day x5 days) and concomitant radiotherapy (45Gy) for five weeks, followed by LapTME or TaTME after 5-8 weeks. Patients who achieved ypT0N0, complete pathological responders (CR) were not treated with adjuvant therapy, according to our Institution policy. Patients with ypT1-2N0, intermediate responders (IR) and ypT3-4 or ypTxN1, poor responders (PR) were offered fluoropyrimidine-based adjuvant treatment on an individual basis. Results: Cohort 1 includes 176 patients from 12/2000 through 12/2008, staged by endoscopic ultrasonography, whereas the cohort 2 included 172 patients from 11/2009 through 12/2015 staged with magnetic resonance imaging. Cohort 1: 171/176 (97.2%) had radical surgery and 19.9% had an abdominoperineal resection (19.9%). The median number of lymph nodes identified in the surgical specimen was 12 (range 0-33). Pathologic complete response (CR) was achieved in 27/171 (15.3%), IR in 47/171 (27%) and PR in 97/171 (55.1%). 11/47 (23%) IR and 47/97 (48%) PR received adjuvant therapy. After a median follow up of 58.3 months (range 3.8-129.8), five-year DFS was 96.3%, 89.4% and 53.6% in the CR, IR and PR groups, respectively (p < 0.0001). Five-year OS was 100% 89.4% and 69.1% in the CR, IR and PR groups, respectively (p < 0.0001). Cohort 2: The presence of EMVI, EMVI+ 72/160 (45%) before neoadjuvant treatment, was associated with a PR (p < 0.0001). Five-year OS was 91.7%, 87.2% and 67.3% in the CR, IR and PR groups, respectively (p = 0.012). Conclusion: Our long term oncologic outcomes obtained in rectal patients who achieved ypT0N0 after neoadjuvant treatment and either LapTME or TaTME, does not support the administration of adjuvant therapy.