Treating breast cancer that has started to spread throughout the body with targeted radiotherapy may help patients live longer without the cancer getting worse, according to results from a small randomized controlled trial presented at the European Society of Radiation Therapy Oncology Congress (ESTRO 2026).
Once cancer begins to spread within the body (metastasize), it is generally difficult to treat and survival rates are low. The new study focuses on patients with oligometastatic breast cancer. This means that several small secondary tumors have broken away from the main tumor and started growing elsewhere in the body.
The researchers treated each small metastasis using stereotactic body radiation therapy (SBRT) alongside regular drug therapy. This type of radiation therapy targets tumors by delivering radiation from different angles around the body. The beams meet at the tumor and deliver a very high but very precise dose of radiation to the cancer cells.
The results of the trial were presented by Professor David Krug from the Department of Radiation Oncology at Schleswig-Holstein University Hospital in Kiel, Germany. “Currently, patients with rare metastatic breast cancer are usually treated in the same way as patients with more advanced breast cancer,” she said.
“While we know that stereotactic body radiotherapy is a highly effective tool for cancer in general, its use in patients with oligometastatic breast cancer is limited due to a lack of studies demonstrating benefits beyond local treatment effects. This means that it may shrink or slow the growth of targeted secondary tumors, but there is no evidence that it improves overall progression-free survival.”
The trial involved 87 patients treated at one of 31 hospitals in Germany and Austria between March 2021 and April 2024. A larger trial was planned, but was canceled early due to slow recruitment. Each patient had 1 to 5 small secondary metastases. Half received standard treatments such as chemotherapy and hormone therapy aimed at controlling the cancer as much as possible. The remaining half received standard treatment and SBRT for each secondary metastasis.
Researchers monitored patients to see if they survived and if the cancer continued to grow or spread. They also assessed patients’ quality of life 12 weeks after radiotherapy treatment using a standard questionnaire.
Patients who received radiation therapy that targeted the secondary tumor lived an average of 36.2 months (median) without their cancer getting worse (progression-free survival). This was 20.6 months for patients who did not receive targeted radiotherapy. This equates to about half the risk of cancer progression or death.
Quality of life measures were similar between the two groups, with an average deterioration of approximately 2 points on a 0-100 scale in the radiotherapy group, well below the predefined margin of 10 points.
The addition of radiotherapy to these small secondary tumors meant that, on average, patients could survive longer without their cancer worsening. Importantly, there was no significant impact on patients’ quality of life. ”
Professor David Krug, Department of Radiation Oncology, University Hospital Schleswig-Holstein, Kiel, Germany.
However, the researchers cautioned that the trial was smaller than they had hoped. Dr. Krug said, “Patient recruitment has been slower than expected, and there are several possible reasons for this. Many patients have too many secondary tumors by the time cancer spread is detected, making this treatment unsuitable for them. Also, patients have not heard of its potential benefits. “We also found that patients often wanted to receive radiation therapy because they knew they could be randomized to standard treatment without radiation therapy, and instead asked to receive radiation therapy outside of the trial.”
Dr. Krug said results from further clinical trials are needed to better understand the effectiveness of targeted radiation therapy in treating oligometastatic breast cancer.
“Stereotactic body radiotherapy is a highly precise treatment that destroys cancer cells while protecting the rest of the body,” said ESTRO Chairman Professor Matthias Guckenberger, from the University Hospital Zurich, Switzerland. Ordinary life.
“While intensive radiation therapy for oligometastatic cancer is well established in other cancer types, such as prostate and lung cancer, previous experience in breast cancer trials has been disappointing. Although this study is small and inconclusive, it offers new hope for breast cancer patients.”
“Results from further trials are expected within the next few years. In the meantime, this treatment may be considered on a case-by-case basis after thorough discussion between patients and doctors.”
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European Society of Radiation Therapy Oncology (ESTRO)
