A small phase I clinical trial concludes that stereotactic ablative radiotherapy (SABR) delivered in five sessions is a safe and well-tolerated treatment for older or frail women with early-stage breast cancer who cannot undergo surgery or decline it. The highest dose studied, 40 Gy in five fractions, produced no dose-limiting adverse effects.
What was known
A significant share of elderly patients with early-stage breast cancer are not surgical candidates or refuse surgery. In them, exclusive hormone therapy offers poor local control, so non-invasive yet effective alternatives were lacking.
What this work adds
This is a single-centre, single-arm phase I trial using a Fibonacci (3 + 3) dose-escalation design. It enrolled people aged 70 or older with a single T1-2 N0 M0-1 tumour deemed inoperable or refused by the patient. SABR was delivered to the primary tumour in five fractions, at three dose levels: 36 Gy, 38 Gy and 40 Gy. The primary endpoint was dose-limiting adverse effects — any grade 3 or higher event in the first six months — with local control, progression-free survival and overall survival as secondary endpoints.
Main results
Between March 2021 and March 2024, 10 patients (11 tumours) were enrolled with a median age of 91 years (range 83-96). Three received 36 Gy, three received 38 Gy and four received 40 Gy. With a median follow-up of 27 months (range 4-40), no dose-limiting adverse events were observed in any cohort, so the maximum tolerated dose was not reached. No acute adverse events were recorded. The only late effect was one case (10%) of grade 1 subcutaneous fibrosis at six months in the 36 Gy level. Cosmetic outcome was excellent or good in 100% of patients. At 24 months, local control, progression-free survival and overall survival were 100%, 90% and 90%, respectively.
What it means
The authors conclude that definitive SABR is an exceptionally safe and well-tolerated procedure in this selected group, with promising preliminary efficacy, and that it stands as a non-invasive alternative to surgery or exclusive hormone therapy. It should be remembered that this is a phase I study with very few patients whose aim was to test safety rather than prove efficacy: the authors themselves call for phase II studies to confirm it. For a patient or a breast unit, the message is that this option still belongs within the framework of clinical research.
Spanish context
The study comes from a Spanish group and addresses a frequent problem in breast units: the management of early tumours in older or frail people for whom surgery may not be advisable. The availability of ablative radiotherapy techniques depends on the technological resources of each radiation oncology service, a factor that shapes equitable access to such treatments within the public system.
Reference: De la Pinta C, Gamero V, Muriel A, Capuz AB, Moris R, Martin M, et al. Phase I study of stereotactic ablative radiotherapy (SABR) in inoperable breast cancer. Breast, 2026. https://doi.org/10.1016/j.breast.2026.104787
