OPERA: CXB boost improves organ preservation in early rectal adenocarcinoma

A contact X-ray brachytherapy (CXB) dose escalation enhances the organ preservation (OP) rate of patients with early rectal adenocarcinoma, with good bowel function at 3 years, results of the OPERA trial have shown. This benefit persists at year 5, particularly in those with small early-stage tumours.

A total of 141 patients with cT2-cT3b low-mid rectal adenocarcinoma, tumours <5 cm, cN0 or cN1 <8 mm were included in this phase III trial. All of them received external beam radiotherapy (EBRT): 45 Gy in 25 fractions with concurrent capecitabine. Participants were then randomized 1:1 to receive either a boost of EBRT (9 Gy/5 fractions; group A) or a boost with CXB (990 Gy/3 fractions; group B).

Forty-four patients in group A and 66 in group B (64 percent vs 92 percent; p<0.001) achieved a clinical complete (or near) response between weeks 14 and 24. At 3 years, the OP rates were 59 percent and 81 percent in groups A and B, respectively (p=0.003).

Over a median follow-up of 61.1 months, the 5-year local regrowth rate was 39 percent in group A and 17 percent in group B (p=0.1).

The significant difference in OP persisted between both groups (56 percent vs 79 percent; p=0.004). This difference was more significant in patients with tumours <3 cm, with an OP rate of 54 percent in group A and 93 percent in group B. Some 28 local regrowths were recorded, of which three occurred after 3 years of follow-up.

“The occurrence of some local regrowth after 3 years necessitates close surveillance of these patients during the 5-year period,” the investigators said.

During follow-up, the most prevalent toxicity seen was rectal bleeding (grade 1‒2), but this disappeared most of the time after 3 years. Notably, CXB boost did not worsen bowel function.