This study is looking at whether a new treatment called KORTUC can safely and effectively help radiotherapy work better at destroying large breast tumours that can’t be removed with surgery. If the early results in breast cancer are positive, the treatment could later be studied in bigger trials and in other hard‑to‑treat cancers.

The study protocol was designed with help from Independent Cancer Patients’ Voice, ensuring the patient perspective was included throughout.

In this phase II trial, we want to find out whether adding KORTUC to standard radiotherapy increases the chance of the tumour disappearing completely, compared with radiotherapy alone.

How KORTUC works:

• KORTUC is given as a direct injection into the tumour before your radiotherapy sessions.

• It contains hydrogen peroxide, which quickly breaks down into water and oxygen once inside the body.

• By mixing it with a special gel, the oxygen is released slowly for more than 24 hours.

• This helps increase the oxygen levels in the tumour, making the cancer cells more sensitive to radiotherapy.

Radiotherapy works best when tumours have enough oxygen. Many cancers are “hypoxic,” meaning they have low oxygen levels, which can make treatment less effective. By improving the oxygen supply, KORTUC may help radiotherapy destroy more cancer cells and may also boost the natural immune response triggered by radiation.

Patient enrolling on this study will require CT scan guided injections of the KORTUC drug into their tumour prior to certain radiotherapy appointments. You will not have any standard treatments delayed or withheld as part of this study.