692 Background: Retrospective case series suggest that watch-and-wait (WW) is a safe alternative to total mesorectal excision (TME) in selected patients with a clinical complete response (cCR) after chemoradiotherapy (CRT). Because treatment strategies vary widely and total numbers of patients treated at different institutions have not been reported, the proportion of rectal cancer patients who can potentially benefit from WW is not known. Here, we report the results of a treatment strategy incorporating WW in a cohort of rectal cancer patients treated with total neoadjuvant therapy (TNT). Methods: Consecutive patients with stage II/III (MRI staging) rectal adenocarcinoma treated with TNT from 2012 to 2017 by a single surgeon were included. TNT consisted of mFOLFOX6 (8 cycles) or CapeOX (5 cycles) either before or after CRT (5600 cGy in 28 fractions with sensitizing fluorouracil or capecitabine). Tumor response was assessed with a digital rectal exam, endoscopy, and MRI according to predefined criteria. Patients with a cCR were offered WW, and patients with residual tumor were offered TME. WW and TME patients were compared based on intention to treat, using the chi-square or rank sum test. Relapse-free survival (RFS) was evaluated by Kaplan-Meier analysis. Results: A total of 109 patients were identified. One patient died during CRT. Of the 108 patients, 64 (59%) had an incomplete clinical response; 4 of the 64 patients declined surgery or had local excision, and 60 underwent TME. The remaining 44 patients (41%) had a cCR and underwent WW. On average, patients in the WW group were older and had smaller, more distal tumors. Median radiation dose, number of chemotherapy cycles, number ofadverse events, or length of follow-up (28 months) did not differ between the TME and WW groups. Five (11%) of the 44 WW patients had local tumor regrowth, at a median of 14 (4–25) months after TNT; 2 of the 5 also had distant metastasis. Six (10%) of the 60 TME patients had a pathological complete response. RFS did not differ between the TME and WW groups (log rank P= 0.09). Conclusions: Approximately 40% of patients with stage II/III rectal cancer treated with TNT achieve a clinical complete response and can benefit from a WW approach with the aim of preserving the rectum.
LBA P-298 Response to total neoadjuvant therapy and survival in patients with early onset locally advanced rectal cancer
