STELLAR II trial at ESTRO 2025: Immunotherapy Combined with Radiotherapy and Chemotherapy Reduces the Need for Surgery in Locally Advanced Rectal Cancer

Vienna, Austria — A new STELLAR II trial presented at ESTRO 2025 reveals that adding immunotherapy to standard radiotherapy and chemotherapy significantly boosts the rate of complete tumour disappearance in patients with rectal cancer—potentially allowing many to avoid surgery and preserve quality of life.

A New Approach to Rectal Cancer Treatment

For patients with locally advanced rectal cancer, the current standard of care includes chemotherapy and radiotherapy followed by surgery. While effective, surgery often results in long-term complications such as reduced sexual function and, in some cases, permanent colostomies—greatly affecting patients’ quality of life.

Now, findings from the STELLAR II trial, a large, multicentre, randomised phase II/III study conducted in China, suggest that incorporating immunotherapy into standard treatment may significantly improve outcomes. The study used sintilimab, a PD-1 inhibitor designed to help the immune system more effectively target cancer cells.

In the trial, one group of patients received standard care—short-course radiotherapy and chemotherapy—while another group received the same treatment plus immunotherapy. The results were striking:

• 45.5% of patients in the immunotherapy group achieved complete tumour disappearance

• Compared to only 25.0% in the standard treatment group

“The findings represent a potential advancement in rectal cancer treatment. Combining immunotherapy with short-course radiotherapy and chemotherapy may improve survival rates and help more patients avoid invasive surgery and its associated long-term effects.”

A Potential Shift in Cancer Treatment

While the addition of immunotherapy was associated with slightly more side effects, researchers noted that they were generally manageable. The study is now continuing in phase III to assess whether the combination leads to improved long-term survival.

Professor Matthias Guckenberger, President of ESTRO and Chair of the Department of Radiation Oncology at the University Hospital Zurich, emphasized the potential impact of these findings:

“This research highlights the potential of combining radiotherapy with immunotherapy in the treatment of rectal cancer. Radiotherapy continues to play a key role, and its integration with immunotherapy presents a promising approach that may help more patients avoid surgery and experience improved outcomes. If validated in larger trials, this strategy could influence future rectal cancer care and contribute to enhancing patients’ quality of life.”

About ESTRO 2025

ESTRO 2025 brings together around 7,000 participants from over 80 countries, showcasing the latest research in clinical radiation oncology, radiobiology, medical physics, technology, and brachytherapy. Leading doctors and scientists from around the world present groundbreaking findings, in line with the conference theme: “Transformative innovation through collaboration”. ESTRO 2025 is the annual congress of the European Society for Radiotherapy and Oncology (ESTRO), an organisation dedicated to advancing cancer treatment through radiotherapy and multimodal approaches. ESTRO promotes education, science, and research and advocates for universal access to radiotherapy. With nearly 10,000 members worldwide, it supports radiation oncology professionals and the broader oncology community in their daily practice.

Read ESTRO 2025 Updates on OncoDaily