Chemoradiotherapy Preserves the Rectum in 78.5% of Patients at 1 Year

Patients with early-stage and intermediate-stage rectal cancer were more likely to keep their rectum 12 months after starting long-course chemoradiotherapy than after short-course radiotherapy, according to results from the phase 2/3 STAR-TREC trial.

Standard treatment for the disease is total mesorectal excision (TME), an operation that removes the rectum along with the fatty tissue around it. The operation controls the cancer well, but it can bring complications around the time of surgery, lasting bowel problems, a permanent stoma (an opening in the abdomen that lets waste pass into a pouch) and a lower quality of life. STAR-TREC tested whether radiation given first could let patients keep the rectum, using a response-adapted plan in which the next step depends on how much the tumor shrinks.

"These early results support a response-adapted organ-preservation approach," wrote the study authors, led by Simon P. Bach, a professor in the Division of Surgery and Interventional Science at University College London in London.

How did long-course chemoradiotherapy compare with short-course radiotherapy in the STAR-TREC rectal cancer trial?

At 12 months, an estimated 78.5% of participants who received long-course chemoradiotherapy were alive and had not had the rectum removed, compared with 60.6% of participants who received short-course radiotherapy. The end point behind the figures is TME-free survival, which counted the time from the start of treatment until death or removal of the rectum.

The comparison produced a hazard ratio of 1.90, a number that describes how often the two groups reached one of those events over time. The trial's statistical model put the probability that long-course chemoradiotherapy was the superior option at more than 99.5%.

At the second response check, 16 to 20 weeks after treatment began, examinations found no remaining sign of the tumor in 104 participants (64%) given long-course chemoradiotherapy and 61 participants (36%) given short-course radiotherapy. Participants with no remaining sign of the tumor moved to a watch-and-wait approach, with regular exams, endoscopy and MRI instead of surgery.

Watch-and-wait monitoring was used in 93 participants (57%) after long-course chemoradiotherapy and 53 participants (32%) after short-course radiotherapy. A smaller operation that removes the tumor site through the anus, called transanal local excision, was needed in 32 participants (20%) and 52 participants (31%), respectively.

Before monitoring began, 82 participants (25%) assigned to keep the rectum went on to have it removed, including 27 (17%) after long-course chemoradiotherapy and 55 (33%) after short-course radiotherapy. Tumor still reaching the muscle wall of the rectum or beyond was found in 24 participants (15%) and 62 participants (37%), respectively.

Intensive chemotherapy and radiation given before surgery has become central to preserving the rectum in more advanced rectal cancer, though the same approach might overtreat early-stage and intermediate-stage disease, the authors explained. In earlier-stage disease, "avoiding unnecessary [surgery to remove the rectum] might be the more appropriate strategy," Bach and colleagues noted.

Who took part in the STAR-TREC trial and how was it designed?

STAR-TREC is an open-label trial, meaning participants and investigators knew which treatment was given. Eligible participants had biopsy-confirmed rectal adenocarcinoma smaller than 40 mm, staged on MRI as mrT1-T3bN0, which describes a tumor confined to the rectal wall or reaching a short distance beyond it with no sign of cancer in nearby lymph nodes. Participants were at least 16 years old in the United Kingdom and at least 18 elsewhere, and they were well enough to carry out daily activities with little or no restriction, measured as an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

Long-course chemoradiotherapy consisted of 50 Gy of radiation in 25 sessions, given with capecitabine, a chemotherapy taken by mouth, at 825 mg/m² twice daily on radiation days. Short-course radiotherapy consisted of 25 Gy in five sessions with no chemotherapy afterward.

In phase 2, participants were randomly assigned in equal numbers to long-course chemoradiotherapy, short-course radiotherapy or immediate surgery to remove the rectum. In phase 3, participants chose between organ preservation and surgery, and the ones who chose organ preservation were randomly assigned to one of the two radiation approaches.

The trial's primary end point has not been reported yet. The measure is successful organ preservation 30 months after treatment starts, defined as no removal of the rectum, no stoma and no return of the cancer in the same area.

What side effects were reported in the STAR-TREC rectal cancer trial?

Serious side effects of grade 3 or worse, meaning severe or life-threatening, occurred over 12 months in 28 of 331 participants (8%) assigned to keep the rectum and 15 of 78 participants (19%) who had immediate surgery.

Grade 3, 4 and 5 serious side effects occurred in 7%, 1% and 0% of the long-course chemoradiotherapy group, 8%, 1% and 0% of the short-course radiotherapy group and 14%, 3% and 1% of the immediate surgery group, respectively.

The most common grade 3-4 serious side effects were stomach and bowel problems, reported in four participants (2%) given long-course chemoradiotherapy, six participants (4%) given short-course radiotherapy and six participants (8%) who had immediate surgery. Complications from procedures followed, reported in three participants (2%), five participants (3%) and five participants (6%), respectively.

Within four weeks of finishing radiation, serious side effects of grade 3 or worse occurred in nine of 163 participants (6%) given long-course chemoradiotherapy and two of 168 participants (1%) given short-course radiotherapy.

A leak where the bowel had been reconnected caused a perforation into the abdominal cavity in 12 participants (15%) who had immediate surgery. One participant who chose immediate surgery died after such a leak, the only death during the 12-month reporting period.

Among participants who did not have a stoma, bowel function at 12 months was better in the groups that kept the rectum than in the group that had it removed. Embarrassment over bowel function worsened at three months in the immediate surgery group and worsened moderately across all groups by 12 months.

"Longer follow-up is needed for the prespecified 30-month [end point]," Bach and coauthors concluded. The next analysis of cancer outcomes is planned at 36 months, followed by a definitive analysis at 60 months.

References

1. Bach SP, et al. "Chemoradiotherapy versus short-course radiotherapy for response-adapted organ preservation in early-stage and intermediate-stage rectal cancer (STAR-TREC): 12-month results of an international, multicentre, open-label, parallel-group, randomised, phase 2/3 trial." The Lancet Oncology. Published Aug. 23, 2026.

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