Breast cancer: shorter radiotherapy becomes the new global standard

By Elodie Vaz | Published on March 12, 2026 | 4 min read


Breast cancer remains the most common cancer in women. In France, around 60,000 new cases are diagnosed each year, about one third of them at the locoregional stage. In these situations, treatment classically relies on surgery followed by radiotherapy targeting the breast or chest wall as well as the lymph node areas.

Until recently, the reference regimen consisted of 25 radiotherapy sessions delivered over five weeks. The final results of a French phase III trial, published in March 2026 in The Lancet after five years of follow-up, could profoundly change this therapeutic strategy worldwide.

Can patients be treated just as effectively in less time?

Coordinated by Dr. Sofia Rivera, radiation oncologist at Gustave Roussy Institute, the HypoG-01 study aimed to evaluate whether a shorter hypofractionated radiotherapy protocol could be used in patients requiring nodal irradiation.

The primary objective was to demonstrate the non-inferiority of a three-week treatment compared with the standard five-week protocol in terms of safety and efficacy. Investigators also sought to determine whether increasing the dose per fraction could raise the risk of lymphedema.

The HypoG-01 trial was conducted in 29 French hospitals and included 1,265 patients between September 2016 and March 2020. All had locoregional breast cancer with lymph node involvement. Inclusion criteria were intentionally broad to reflect the diversity of clinical situations encountered in practice, including different tumor subtypes (HER2-positive, hormone-receptor-positive, or triple-negative cancers).

“Our ambition was to develop a pragmatic trial whose conclusions could easily be applied in routine clinical practice,” said Dr. Sofia Rivera in a press release from Gustave Roussy Institute. Participants were randomized into two groups. The first received a hypofractionated protocol of 15 sessions over three weeks, for a total dose of 40 Gy (2.67 Gy per fraction). The second group followed the standard treatment of 25 sessions over five weeks, for a total dose of 50 Gy (2 Gy per fraction). Statistical analyses were performed by the team of Prof. Stefan Michiels, a biostatistics specialist at Gustave Roussy.

Three weeks of treatment as safe as five

After five years of follow-up, results show that three-week hypofractionated radiotherapy has a safety profile comparable to the standard treatment. The incidence of lymphedema is almost identical in both groups: 22% in the conventional treatment arm versus 23% in the hypofractionated group. Serious adverse events remain rare and similar between the two strategies (2.6%).

The study also confirms the oncological effectiveness of the shorter protocol. The three-week regimen is not less effective than the standard treatment in preventing recurrences and ensuring equivalent chances of cure.

These data provide a particularly important level of evidence for nodal irradiation, especially for internal mammary chain nodes, which are located deeper in the chest and have historically been considered more challenging to treat with hypofractionation.

Beyond the scientific demonstration, the clinical and organizational impact of these findings is considerable. Reducing radiotherapy from 25 to 15 sessions shortens treatment duration by 40%, significantly easing the burden for both patients and healthcare systems.

“The HypoG-01 study finally provides the high-level scientific evidence we were lacking internationally to generalize shorter treatment for breast cancers requiring nodal irradiation,” said Dr. Sofia Rivera. “We demonstrate that it is possible to treat just as effectively—but much faster—by reducing the treatment pathway for women by two weeks without any increased risk of complications.”

Toward more efficient radiotherapy

By establishing the non-inferiority of a hypofractionated protocol in breast cancers with lymph node involvement, the HypoG-01 trial marks a major step in the evolution of therapeutic standards. Promoted by Unicancer and supported by the French National Cancer Institute (INCa), this French academic research paves the way for a broader transformation of breast radiotherapy.

Beyond improving the care pathway, these results could also facilitate access to radiotherapy in constrained healthcare systems where equipment availability and treatment slots remain limited. In the future, the integration of even more personalized irradiation strategies, combined with advances in precision radiotherapy, could continue this trend

Read next: Combined exercise: a winning strategy for post–breast cancer cardiorespiratory fitness

About the Author – Elodie Vaz
Health journalist, CFPJ graduate (2023).
Élodie explores the marks diseases leave on bodies and, more broadly, on human life. A registered nurse since 2010, she spent twelve years at patients’ bedsides before exchanging her stethoscope for a notebook. She now investigates the links between environment and health, convinced that the vitality of life cannot be reduced to that of human.