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Purpose <p>Postmastectomy radiotherapy (PMRT) reduces locoregional recurrence and improves survival in high-risk breast cancer (BC), yet its real-world use remains variable. Population-based data on PMRT utilization and guideline adherence in Switzerland are lacking. We evaluated PMRT patterns, determinants, and adherence to ASCO-ASTRO-SSO recommendations among women with stage I–III BC over two time periods and interpreted findings in the context of the 2025 guideline.</p> Methods <p>This retrospective, population-based study analyzed data from seven Swiss cancer registries, including Eastern Switzerland (2003–2005; <i>n</i> = 4,246), and from Eastern Switzerland alone (2015–2017; <i>n</i> = 976). Eligible patients were women aged ≥ 18&#xa0;years with stage I–III invasive BC treated by simple mastectomy. PMRT use was examined across original ASCO-ASTRO-SSO-defined risk groups: low-risk (T1–2N0), intermediate-risk (T1–2N1, T3N0), and high-risk (T4 or N2–3). Multivariable regression identified clinicopathologic determinants of PMRT use. Trends in PMRT guideline adherence and regional nodal irradiation (RNI) were evaluated within the framework of evolving clinicobiologic risk paradigms. Overall survival (OS) was analyzed using Kaplan–Meier and Cox regression methods.</p> Results <p>Overall PMRT utilization remained low (25–30%) across both periods. PMRT was independently associated with younger age, higher T-/N-stage, lymphovascular invasion (<i>p</i> &lt; 0.01), positive margins, G3 histology, and ER negativity (<i>p</i> &lt; 0.05). Adherence to guidelines improved in low-risk patients (93% to 96%) but declined in high-risk patients (64% to 54%), with decreasing PMRT use in T4 (53% to 27%), N2 (73% to 57%), and N3 disease (83% to 73%). In contrast, PMRT use increased among intermediate-risk patients (23% to 39%), particularly in T1–2N1 disease (19% to 38%) and in the presence of adverse features: LVI + (21%), HER2 + (23%), TNBC (30%), G3 (38%), and age &lt; 45&#xa0;years (57%). Supraclavicular/axillary RNI declined overall but increased in node-negative patients, paralleling reduced axillary dissection and increased sentinel biopsy (26% to 70%). PMRT was not associated with a statistically significant OS benefit; supraclavicular RNI showed a non-significant trend toward improved OS in N2–3 disease.</p> Conclusions <p>This first national analysis provides real-world evidence that PMRT utilization in Switzerland remains low, with underuse in high-risk patients and selective, biologically informed escalation in intermediate-risk disease. While patterns reflect evolving multidisciplinary care, persistent gaps in ASCO-ASTRO-SSO guideline implementation underscore the need for continued surveillance and individualized, risk-adapted PMRT decision-making.</p>

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Trends in postmastectomy radiotherapy for early and locally advanced breast cancer in Switzerland: a population-based cross-sectional and longitudinal analysis

  • 期刊论文

  • 发表日期：

    2026年1月13日

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  • Marcel Blum,
  • Sonja Marion Koch,
  • Mohsen Mousavi,
  • Denise Vorburger,
  • Andreas Müller,
  • Michel Eric Nicolas Zimmermann,
  • Christoph Oehler,
  • Daniel Rudolf Zwahlen

摘要

Purpose

Postmastectomy radiotherapy (PMRT) reduces locoregional recurrence and improves survival in high-risk breast cancer (BC), yet its real-world use remains variable. Population-based data on PMRT utilization and guideline adherence in Switzerland are lacking. We evaluated PMRT patterns, determinants, and adherence to ASCO-ASTRO-SSO recommendations among women with stage I–III BC over two time periods and interpreted findings in the context of the 2025 guideline.

Methods

This retrospective, population-based study analyzed data from seven Swiss cancer registries, including Eastern Switzerland (2003–2005; n = 4,246), and from Eastern Switzerland alone (2015–2017; n = 976). Eligible patients were women aged ≥ 18 years with stage I–III invasive BC treated by simple mastectomy. PMRT use was examined across original ASCO-ASTRO-SSO-defined risk groups: low-risk (T1–2N0), intermediate-risk (T1–2N1, T3N0), and high-risk (T4 or N2–3). Multivariable regression identified clinicopathologic determinants of PMRT use. Trends in PMRT guideline adherence and regional nodal irradiation (RNI) were evaluated within the framework of evolving clinicobiologic risk paradigms. Overall survival (OS) was analyzed using Kaplan–Meier and Cox regression methods.

Results

Overall PMRT utilization remained low (25–30%) across both periods. PMRT was independently associated with younger age, higher T-/N-stage, lymphovascular invasion (p < 0.01), positive margins, G3 histology, and ER negativity (p < 0.05). Adherence to guidelines improved in low-risk patients (93% to 96%) but declined in high-risk patients (64% to 54%), with decreasing PMRT use in T4 (53% to 27%), N2 (73% to 57%), and N3 disease (83% to 73%). In contrast, PMRT use increased among intermediate-risk patients (23% to 39%), particularly in T1–2N1 disease (19% to 38%) and in the presence of adverse features: LVI + (21%), HER2 + (23%), TNBC (30%), G3 (38%), and age < 45 years (57%). Supraclavicular/axillary RNI declined overall but increased in node-negative patients, paralleling reduced axillary dissection and increased sentinel biopsy (26% to 70%). PMRT was not associated with a statistically significant OS benefit; supraclavicular RNI showed a non-significant trend toward improved OS in N2–3 disease.

Conclusions

This first national analysis provides real-world evidence that PMRT utilization in Switzerland remains low, with underuse in high-risk patients and selective, biologically informed escalation in intermediate-risk disease. While patterns reflect evolving multidisciplinary care, persistent gaps in ASCO-ASTRO-SSO guideline implementation underscore the need for continued surveillance and individualized, risk-adapted PMRT decision-making.