SABR for Bone Metastases 2025 Study Summary

Introduction

This summary unpacks the latest small-scale (2025) research and insights on stereotactic ablative radiotherapy (SABR) for breast cancer that has spread only to the bones (bone-only oligometastatic disease, or OMD)

What Was Studied?

Researchers looked at 47 women with breast cancer whose cancer had spread to up to five bone sites, but not to other organs. All patients received SABR—a highly targeted, high-dose form of radiation—on all bone metastases. The study aimed to determine which patients benefit most from SABR and what factors affect outcomes.

Why Is This Important?

• Bone-only metastasis often has a better outlook than when cancer spreads to other organs.

• SABR can precisely target cancer in the bones, potentially improving survival and quality of life with fewer side effects.

• Understanding which patients benefit most helps tailor treatment and avoid unnecessary therapies.

Key Findings

Survival and Disease Control

• 2-year overall survival: 90%

• 5-year overall survival: 66%

• 2-year progression-free survival: 49%

• 5-year progression-free survival: 29%

• Local control at treated bone sites: 85%

Who Did Best?

• HER2-enriched subtype: All patients with this subtype were alive at 5 years.

• Synchronous metastases: Patients whose bone metastases appeared at the same time as their initial diagnosis had better survival.

• No prior widespread metastases: Patients who had not previously had widespread disease did better.

• Phenotypic discordance: Patients whose cancer subtype changed between the original tumour and the bone metastasis had worse outcomes, with 0% progression-free survival at 5 years.

Safety

• SABR was generally well tolerated.

• No severe (grade 4) side effects were reported.

• Some patients experienced mild to moderate pain or bone fractures, which were manageable.

Understanding SABR Dosing: 

SABR is designed to deliver a precise, concentrated (high) radiation dose to a tumour in a small number of treatments (fractions). Compared to conventional radiotherapy, SABR uses fewer sessions but with a higher dose per session. In this study, the median dose was 30 Gy (range, 12–40 Gy) delivered in a median of 5 (range, 1–5) fractions, with a median biologically effective dose (BED4) of 75 Gy1.

• Typical SABR regimens for bone metastases:

  • Single fraction: 18–20 Gy in 1 session

  • Three fractions: 30 Gy in 3 sessions (10 Gy per session)

  • Five fractions: 35 Gy in 5 sessions (7 Gy per session)

Key points:

• SABR is almost always "high dose" per session compared to standard radiotherapy, but the total number of sessions is much lower.

• The regimen is tailored to each person’s situation, considering tumour size, location, and proximity to sensitive structures.

• The high dose is carefully planned to avoid harming healthy tissue, and adjustments are made if there are risks.

Understanding Phenotypic Discordance

Phenotypic discordance means the cancer’s biological characteristics (like hormone receptor or HER2 status) changed between the original breast tumour and the bone metastasis. This can happen because:

• Different groups of cancer cells may behave differently.

• Treatments can kill off sensitive cells, leaving resistant ones with new features.
  

Why does this matter?

• If the change isn’t detected (for example, if the bone metastasis isn’t biopsied), patients may keep getting drugs that no longer work for their current cancer type.

• This can lead to worse outcomes including the ones seen here, not because SABR is less effective, but because the systemic (whole-body) treatments aren’t properly matched to the cancer’s current biology. Meanwhile, how often are bones being biopsied?

• Tumours that change type are often more challenging to treat.

Do Different Subtypes Respond Differently to Radiation?

Yes. Even when the right drugs are used, breast cancer subtypes can respond differently to radiation:

• Luminal subtypes (hormone receptor-positive) are generally more sensitive to radiation.
  

• HER2-enriched cancers may be more resistant, but combining radiation with HER2-targeted drugs can help.
  

• Triple-negative cancers can be aggressive and unpredictable in their response.
  

What Does This Mean for Patients?

• Personalised Care: Knowing the subtype of both the primary tumour and any metastases is crucial for choosing the best combination of systemic therapy and radiation.

• Biopsy of Metastases: If cancer spreads, a biopsy of the new site can reveal changes in subtype, ensuring treatments are tailored to the current biology.

• Advocate for Yourself: Ask your care team about the possibility of targeted radiation and whether a biopsy of bone metastases is appropriate.

Questions to Discuss With Your Healthcare Team

• Is SABR an option for my type and stage of breast cancer?

• What are the potential benefits and risks of SABR in my situation?

• Should my bone metastases be biopsied to check for changes in cancer type?

• Are there clinical trials or new treatments available for my specific case?

Conclusion

This research shows that SABR can be a valuable treatment for selected breast cancer patients with bone-only, limited metastases. The best results are seen in certain subgroups, especially those with HER2-enriched tumours and no prior widespread disease. However, if the cancer’s characteristics change and this isn’t detected, outcomes may be worse, not because of the radiation, but because systemic treatments may no longer be effective.

Speak with your oncology team to understand how these findings may apply to your situation.

This summary is designed to help patients and advocates understand recent small-scale, yet real-world research. https://ppl-ai-file-upload.s3.amazonaws.com/web/direct-files/attachments/16339349/22c8dc03-c1a9-4b6c-bf46-8e79f2746a93/PIIS0936655524004552.pdf

Group Members Q&A

Q: I thought luminal (hormone receptor-positive) breast cancers are more sensitive to radiation, but in the study, HER2-enriched patients had the best survival. How does that make sense?

A: While luminal subtypes are generally more sensitive to radiation in lab tests, real-world outcomes like survival depend on many factors—not just radio-sensitivity. In this study, HER2-enriched patients likely did better because they received both SABR and effective HER2-targeted therapies, and many had favourable disease features (like bone-only, synchronous metastases). So, even though luminal cancers are more radiosensitive, HER2-enriched patients had the best results here due to the combination of targeted treatments and patient selection. Radiosensitivity is just one piece of the puzzle—clinical outcomes are shaped by the whole treatment approach and the biology of each patient’s cancer.

Likely related pages

• Bone Metastases

• Radiation Post-First-Line Chemo? 2025 Summary

• Post-Chemotherapy Cell Senescence Clean-up