-De-escalating Breast Radiotherapy in the Age of Omission: No Retreat, Baby, No Surrender

Introduction

To omit is not to retreat, and de-escalation is certainly not surrender. Yet in modern breast cancer care, omission has become almost synonymous with radiotherapy. Why?

Breast cancer is the most frequently diagnosed cancer among women in the EU-27, with more than 350,000 new cases each year. Advances in surgery, radiotherapy, and systemic therapies have raised 5-year relative survival to around 83%, based on population data across all disease stages [1]. This remarkable success has created a new challenge: can some patients safely receive less treatment without compromising cure?

“Less is more” has become a defining principle of modern breast cancer care. De-escalation has transformed surgery, from radical mastectomy to breast-conserving surgery, from axillary lymph node dissection to sentinel lymph node biopsy and no sentinel biopsy at all in some cases, and systemic therapy through more effective, less toxic and biologically targeted treatments. Radiotherapy has evolved in parallel, with hypofractionation, partial-breast irradiation and image guidance reducing treatment from six weeks to as little as one. The next frontier is no longer treatment reduction but treatment omission. Yet one fundamental question remains: why is radiotherapy so often the first treatment considered for omission despite substantial biological and technological advances that reduce treatment burden?

Before addressing that question, it is worth recalling five decades of evidence. Across randomized and population-based studies in elderly, younger and unselected women undergoing breast-conserving surgery, adjuvant radiotherapy has consistently halved local recurrence compared with surgery alone or endocrine therapy, in both invasive breast cancer and DCIS [2,3]. Better local control has also translated into improved breast cancer survival [4], including in biologically favorable subtypes such as mucinous carcinoma [5]. The oncological principle therefore remains unchanged: durable cure relies on durable local control [6]. Against this background, landmark trials such as CALGB 9343 and PRIME II did not question the efficacy of radiotherapy but rather whether its incremental benefit in carefully selected low-risk patients was sufficient to justify omission [7,8]. However, a note of caution is warranted. While de-escalation studies understandably attract considerable attention by challenging established practice, positive omission trials often receive greater visibility than negative ones. Ultimately, the key question is not whether radiotherapy reduces local recurrence, which it unequivocally does, but what magnitude of benefit is considered clinically worthwhile, a threshold that may reasonably differ among patients, clinicians, and healthcare systems.

Reduce, adapt: three levers before radiotherapy omission

Omission should be viewed as the last rung of the de-escalation ladder, not its starting point. De-escalation is not simply “doing less,” but rather the personalized optimization of treatment by balancing risks and benefits through stepwise refinement of treatment selection, extent, and combinations [9]. De-escalation should be contemplated as a hierarchical process: first reducing treatment volume through partial-breast irradiation, then treatment duration via hypofractionation, followed by minimizing dose to normal tissues, with omission considered only as the final step within a shared decision-making framework aligned with patient values [10]. Modern radiotherapy provides multiple evidence-based opportunities to reduce treatment burden while preserving efficacy, and these strategies should be fully explored before considering omission:

Reducing the treated volume. Accelerated partial-breast irradiation (APBI) targets the tumor bed with a margin rather than the whole breast. ASTRO, GEC-ESTRO and DEGRO guidelines recommend APBI for carefully selected low-risk patients, typically older women with small, unifocal, hormone receptor-positive, low-grade tumors, negative margins and no adverse pathological features, while excluding higher-risk disease or patients treated with neoadjuvant chemotherapy [11-13]. Randomized trials support this approach: FLORENCE showed that IMRT-based APBI (30 Gy in 5 fractions) achieved 10-year local control comparable to whole-breast irradiation, with less toxicity and better cosmesis; IMPORT LOW confirmed non-inferior 10-year local recurrence with partial-breast irradiation delivering 40 Gy in 15 fractions, and IMPORT HIGH showed that a simultaneous integrated boost (48 Gy in 15 fractions) can shorten treatment while maintaining tumor control and acceptable toxicity [14-16]. Overall, reducing treatment volume can preserve oncological outcomes while improving convenience, limiting toxicity and optimizing resources.

Reducing treatment length. Hypofractionation and ultra-hypofractionation have shortened adjuvant breast radiotherapy from 5–6 weeks to 1–3 weeks, and in selected partial-breast protocols to 5 fractions in 1 week, without compromising local control, cosmesis or toxicity. The FAST-Forward trial established 26 Gy in 5 fractions as a safe standard, with 10-year results showing non-inferior local control and comparable normal tissue effects versus 40 Gy in 15 fractions [17]. Although adoption remains variable, these data support shorter schedules, including regional nodal irradiation, while simultaneous boost integration within one-week schedule is currently being prospectively tested in a randomized clinical trial [18,19].

Reducing dose to healthy tissues is essential before considering RT omission. DIBH and prone positioning reduce cardiac and pulmonary exposure, with prone positioning lowering mean heart dose versus DIBH alone [20,21]. In selected patients at increased cardiac risk, proton therapy further reduces heart, lung and contralateral breast doses, with an estimated 3% absolute reduction in lifetime risk of acute coronary events [22]. RT omission should be considered only after target volumes and normal-tissue doses are optimized, and only using validated predictive, not merely prognostic, biomarkers.

Yet beyond the discussion of adapting, de-escalating, or omitting treatment, one fundamental question remains: who, really, is elderly? Omission trials often define age by arbitrary chronological cut-offs—65, 70, or even 50 years—although age poorly reflects biological fitness. In Spain, women have nearly 18 years of remaining life expectancy at 70 and more than 10 years at 80, with many maintaining good functional status throughout these years [23]. A fit 72-year-old differs markedly from a frail peer with multiple comorbidities, and grouping both as “elderly” risks under- or overtreatment [24]. Since radiotherapy omission still carries a meaningful locoregional recurrence risk, decisions should rely on geriatric assessment, life expectancy and patient preferences, not chronological age alone.

The flip side: should we sometimes omit (all) systemic therapy instead?

If treatment de-escalation is to be applied consistently, omission should not be considered only for radiotherapy. De-escalation strategies are being explored not only for postoperative radiotherapy [25], but also for adjuvant systemic therapy [26] and even surgery after exceptional responses to neoadjuvant treatment [27], reinforcing the principle that omission should be evaluated impartially across all treatment modalities rather than disproportionately targeting radiotherapy.

Kaidar-Person, Walker and Morgan proposed that, particularly in older patients with comorbidities, radiotherapy may be preferable because its benefit is concentrated within the first five years, whereas endocrine therapy relies on delayed effects, long-term adherence and chronic toxicity [28]. Likewise, following the results of PRIME II, the value of prolonged endocrine therapy in older women with an excellent prognosis has also been questioned, given that contemporary radiotherapy provides durable local control with minimal long-term toxicity, whereas endocrine therapy requires five years of treatment without a clear survival advantage in this setting [29]. This illustrates that de-escalation should not focus exclusively on radiotherapy: for example, the NHS Predict model estimates that a 70-year-old woman with a 20-mm, grade 2, HR-positive/HER2-negative tumor derives <1% absolute 5-year overall survival benefit from endocrine therapy, a modest gain that should be balanced against treatment-related adverse effects, including an estimated 1–2% risk of acute myocardial infarction and an overall incidence of severe (grade ≥3) adverse events of approximately 5% (https://breast.v3.predict.cam/tool). Importantly, endocrine therapy should not be regarded as a toxicity-free alternative to radiotherapy. Estrogen deprivation is associated with substantial morbidity, including vasomotor symptoms, fatigue, musculoskeletal toxicity, osteoporosis, with secondary increase in the risk of bone fractures, and metabolic complications, and 30–50% of older women discontinue treatment within five years because of adverse effects, frailty or comorbidity [30]. Consequently, replacing radiotherapy with endocrine therapy assumes sustained adherence that is frequently not achieved in routine practice [31,32].

Patient-reported outcomes are increasingly recognized as key endpoints in modern de-escalation trials and further challenge the perception that endocrine therapy is the less burdensome option. In the preplanned interim analysis of the EUROPA trial, endocrine therapy was associated with significantly worse quality of life and more grade 3–4 adverse events than radiotherapy in women aged ≥70 years with luminal A-like early breast cancer [14]. Ongoing randomized trials, including REaCT (NCT04921137), CAMERAN (NCT05472792) and EMERALD (NCT06897488), will further clarify these trade-offs by prioritizing quality of life and patient-reported outcomes. Ultimately, treatment decisions should be guided not only by recurrence risk but also by informed patient preferences, as equally informed women may reasonably make different choices when balancing modest benefits against treatment burden.

When to omit… everything?

Taken to its logical conclusion, the omission debate extends far beyond radiotherapy or endocrine therapy. Even mammographic screening is increasingly being questioned. Depending on the methodology used, pooled estimates suggest overdiagnosis rates ranging from approximately 11% to more than 50%, with little or no consistent reduction in advanced-stage disease at presentation and only a modest, if any, effect on breast cancer mortality in the era of effective systemic therapy. The UK Independent Breast Screening Review estimated that for every breast cancer death prevented, approximately three women are over diagnosed and treated unnecessarily [33]. Likewise, the 25-year follow-up of the Canadian National Breast Screening Study found that annual mammography in women aged 40–59 years did not reduce mortality beyond that achieved with clinical examination and contemporary adjuvant therapy, while 22% of screen-detected invasive cancers were considered over diagnosed [34]. Population-based studies from Denmark and the Netherlands have similarly suggested that overdiagnosis may affect one-third to one-half of screen-detected cancers [35,36]. If a substantial proportion of the cancers we diagnose would never become clinically relevant, then the most provocative omission question arises even before radiotherapy, endocrine therapy or surgery: are there women who derive no benefit from treatment, or even from the diagnosis itself? [37]

To date, no subgroup of women with low- or very-low-risk breast cancer has been consistently identified in whom radiotherapy after breast-conserving surgery provides no benefit whatsoever. The contemporary omission debate is less about efficacy than about clinical value. That is, whether a modest absolute reduction in recurrence justifies treatment given the patient’s competing risks, preferences, and expected quality of life.

Modern radiotherapy supports treatment de-escalation through optimization and individualization, but de-escalation should not be equated with omission. Radiotherapy remains a cornerstone of breast cancer management, improving not only locoregional control but, in selected settings, overall survival.

Equally important, endocrine therapy is neither toxicity-free nor an automatic substitute for radiotherapy; in carefully selected patients with significant comorbidity, omitting endocrine therapy may be a more rational strategy than omitting radiotherapy. The same rigorous, predictive and patient-centered approach now applied to radiotherapy should also be extended to surgery, systemic therapy and even screening.

The fundamental question is therefore not “when can we omit radiotherapy?” but rather “when can we safely omit anything at all?” The answer should be guided by tumor biology, validated predictive biomarkers, geriatric assessment, patient preferences and patient-reported outcomes, not by chronological age as a surrogate for frailty, nor by cost or convenience disguised as clinical benefit.

De-escalation is not a binary decision but a process of precision medicine: reducing treatment where appropriate while preserving efficacy and quality of life. De-escalation is therefore not omission, but optimization. Precision oncology should ask what the minimum treatment is required to preserve the maximum chance of cure and quality of life. Because in older women with breast cancer, as throughout oncology, the future lies in reduction without retreat, adaptation without surrender, and precision without compromise.

Statements

Author’s contribution: AM, IR and RC conceived and planned the idea for the editorial; AM took the lead in writing the manuscript; AM, IR, and RC read, discussed, provided critical feedback and made the final approval.

Consent for publication: As corresponding author, I confirm that the manuscript has been read and approved for submission by all named authors.

Declaration of interest: The authors declare no conflicts of interest regarding any aspect of this manuscript.

Funding: The authors declare no source of funding for this manuscript.

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