A groundbreaking clinical trial led by researchers at the University of Leeds has found that a reduced dose and shorter course of radiotherapy is as effective as traditional treatment for early-stage anal cancer while causing fewer side effects.
The phase 2 PLATO-ACT4 trial (ISRCTN88455282) demonstrated favorable 6-month complete clinical response rates across both standard and reduced radiotherapy dosing regimens. The findings, published in Lancet Oncology, could transform treatment approaches for this rare cancer that affects approximately 1,600 people annually in the UK.
Comparable Efficacy with Reduced Treatment Burden
In the prospective, non-comparative trial, patients were randomly assigned in a 1:2 ratio to receive either standard-dose intensity-modulated radiotherapy (sd-IMRT) at 50.4 Gy in 28 fractions or reduced-dose IMRT (rd-IMRT) at 41.4 Gy in 23 fractions. Both groups received concurrent mitomycin and capecitabine chemotherapy.
At the 6-month assessment, complete clinical response occurred in 84.4% (135/160) of all evaluable patients. The response rates were nearly identical between the standard-dose arm at 84% (46/55; 95% CI, 71.2%-92.2%) and the reduced-dose arm at 85% (89/105; 95% CI, 76.4%-91.0%).
Long-term results were equally impressive, with 87.6% of patients in the reduced-dose group remaining cancer-free at three years, compared to 83.6% in the standard-dose group.
"The results will transform the lives of patients with early stage anal cancer by using a shorter, lower dose of radiotherapy that does not compromise cure rates and reduces the side effects of treatment," said Professor David Sebag-Montefiore, Chief Investigator of the PLATO study and Audrey and Stanley Burton Professor of Clinical Oncology at the University of Leeds.
Reduced Toxicity and Improved Patient Experience
The trial revealed significant advantages for the reduced-dose approach in terms of treatment-related toxicities. Grade 3 or higher adverse effects occurred in 46% (25/55; 95% CI, 32%-60%) of the standard-dose arm compared to 35% (37/105; 95% CI, 26%-45%) of the reduced-dose arm.
Common severe side effects included radiation dermatitis (13% vs 10%), diarrhea (7% vs 9%), and neutropenia (4% vs 6%) in the standard and reduced-dose arms, respectively. Serious adverse reactions occurred in 15% of standard-dose patients versus 10% of reduced-dose patients. No treatment-related deaths were reported in either group.
Treatment compliance also improved with the reduced-dose regimen. Radiotherapy interruptions lasting 3 days or longer were needed for 26% (14/55) of standard-dose patients compared to only 15% (16/105) of reduced-dose patients. Similarly, chemotherapy modifications were required in 49% (27/55) of standard-dose patients versus 37% (39/105) of reduced-dose patients.
Dr. Alexandra Gilbert, Associate Professor at the University of Leeds, highlighted another important benefit: "We also see a trend towards improved sexual function in the longer term for men and women using the shorter, lower dose treatment."
Patient Perspective
Sam Panter, a 48-year-old RAF veteran and mother of two who participated in the trial, received the standard dose treatment and experienced significant side effects.
"I tolerated my treatment well until about the halfway point, when I started to suffer quite badly from side effects. I had big blisters around the radiotherapy site and a constant feeling of having a urine infection, which was extremely uncomfortable," Panter recalled.
"I remember getting to the halfway point and thinking how am I going to carry on to the end? It had got so uncomfortable, and travelling to and from appointments each day for treatment, which was an hour journey each way, was taking its toll and I had extreme fatigue."
Despite these challenges, Panter successfully completed her treatment and was declared cancer-free after five years of follow-up. She expressed pride in participating in research that could benefit future patients: "I'm so proud to have been part of this work and I really hope it leads to improved treatment options for people around the world who face a diagnosis like me."
Changing Clinical Practice
The PLATO protocol encompasses three individual trials—ACT3, ACT4, and ACT5—designed to optimize radiotherapy dosing in combination with chemotherapy for patients with low-, intermediate-, and high-risk anal cancer.
For the ACT4 trial, eligible patients had histologically confirmed invasive primary squamous, basaloid, or cloacogenic carcinoma of the anus, were at least 16 years old, had adequate bone marrow, hepatic, and renal function, and an ECOG performance status of 0 or 1.
The median age of participants was 66 years (range, 35-87), and 80% (128/160) had T2 tumors with a median size of 2.5 cm. Notably, the benefits of reduced-dose treatment were particularly evident in older patients, with radiotherapy interruptions required in only 15% of those aged 70+ in the reduced-dose arm compared to 36% in the standard-dose arm.
"Given the improvements in compliance and tolerability of the de-escalated regimen in older patients, with preserved early cancer outcomes, this reduced-dose regimen could be considered a new treatment option for [patients who are] frailer [and] not fit for standard-dose chemoradiotherapy," noted lead study author Alexandra Gilbert.
Dr. Iain Foulkes, Executive Director of Research and Innovation at Cancer Research UK, called the results "an outstanding example of harnessing the latest advances in radiotherapy technology to target cancer cells and minimise side effects and personalise radiotherapy treatment in this rare disease."
The findings were presented at ESTRO 2025 (European Society for Radiotherapy and Oncology congress) and have been hailed as practice-changing by the international oncology community.
Future Directions
While the primary endpoint of 3-year locoregional failure data is still pending in the ACT4 study, the current results strongly suggest that the reduced-dose approach could become the new standard of care for early-stage anal cancer.
Professor Sebag-Montefiore emphasized the broader implications: "The current approach for anal cancer treatments is essentially a 'one size fits all' where the dose of radiotherapy is similar whether the tumour being treated is very small or very large. These results are a major breakthrough... The shorter, highly effective radiotherapy course not only reduces side effects, it reduces hospital visits and optimises the use of healthcare resources."
After 30 years of largely unchanged treatment approaches, this personalized strategy represents a significant advancement that could improve outcomes and quality of life for anal cancer patients worldwide.
