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The OPERA trial (NCT02505750)) was designed in 2014 to test the hypothesis that a Contact X Ray Brachytherapy 50kV (CXB) boost, preceding/following chemoradiotherapy  (CRT) was able to increase the 3-year rate of organ preservation (OP),primary end point, for tumours of low-mid rectum.

Inclusion was : All age, cT2-T3 < 5cm Ø < 50% circumference, cN0-1 (< 8mm).  Classification with MRI. All patients received neoadjuvant CRT (cape 45). Boost was randomised 1 :1 between Arm A : EBRT 9 Gy/fr. against Arm B : CXB 90 Gy/3 fr.Stratification separated T< 3cm (A1/B) vs ≥ 3cm (A2/B2) with CXB given first for B1. Response evaluation was made at week, 14, 20, 24 after treatment start using palpation, endoscopy ,  MRi.

Between 5-2015/6-2020, 141 patients were included with intent to treat. Good balance between arms was observed : median age 69, Men : 87, Distal rectum :106, T2/T3 : 91/50, N0/1 : 106/35. Observance to all treatments was good in≥94%. Median follow-up time (May 2021) was 38 months. Between week 14-24, a clinical complete (or near) response ncCR was observed in 44 patients in A (65.7%) vs 66 in B (94.3%) ; p<0.001. A TME surgery was performed in 39 patients (A : 26/B : 13).The OP rate was significantly increased in B (81%) vs A (59%) and still more in B1 vs A1 (97% vs 63%) (figure). No toxicity difference was seen between A and B (40, 4% grade 2-3) late, mild  rectal bleeding was more frequent in B vs A (76% vs 23%). Bowel function was good in > 80% for both arms. These results will be updated with 4-year follow-up at time of the meeeting with additionnal data regarding MRI, Local excision and immunoscore.

The OPERA trial is the first to demonstrate that a CXB dose escalation is increasing the OP rate with good bowel function. This benefit is optimal if starting treatment in T < 3cm using CXB first. Such a planned rectal preservation appears as a valid option to discuss in MDT and with well informed patient for select tumor and prolonged surveillance after watch and wait.