S298
Clinical - Breast
ESTRO 2026
recurrence was classified according to its location relative to the clinical target volume (CTV) according to ESTRO guidelines as in-field, (inside the irradiated CTV), marginal (outside the irradiated CTV with >50% prescribed dose), or distant. Clinical, pathological, and treatment characteristics of patients with an event were collected to identify potential factors associated with different recurrence types. For each locoregional recurrence, imaging used to identify relapse was compared with the initial simulation CT to estimate delivered dose. Results: After a median follow-up of 4.8 years, 120 patients experienced recurrence or a second malignancy. Twenty-seven had LRR (20 isolated, 7 concomitants with distant relapse) and 59 had isolated distant recurrence. Most regional failures involved level I (37.5%) and level II (20.8%) lymph nodes. Left-sided tumours (77.8% vs. 47.5%, p = 0.01) and breast- conserving surgery (74.1% vs. 45.8%, p = 0.02) were more frequently associated with LRR. Among patients with LRR, there were 41 recurrences sites. Twenty-nine LRR were considered in-field, with all but one receiving >95% of the prescribed dose. Among the 9 marginal recurrences, 8 were located inside ESTRO CTV despite not being planned for irradiation: 3 received at least 95% of the prescribed dose and 5 received less than 95% of it. Only one marginal recurrence occurred outside the ESTRO CTV but received >95% of the prescribed dose.
Proffered Paper 3330
Patterns of locoregional and distant recurrence and dosimetric analysis in the HypoG-01 phase III trial Louis Munschi 1 , Robabeh Ghodssighassemabadi 2 , Guillaume Auzac 3 , Youlia Kirova 4 , Mohamed Benchalal 5 , Claire Charra Brunaud 6 , Séverine Racadot 7 , Ahmed Benyoucef 8 , Delphine Argo 9 , Claire Lemanski 10 , David Pasquier 11 , Karine Peignaux 12 , Aurore Goineau 13 , Agnes Tallet 14 , Philippe Guilbert 1 , Adeline Petit 15 , Aurélie Bellière 16 , Jean-Baptiste Clavier 17 , Marie-Eve Fouche-Chand 18 , Yazid Belkacemi 19 , Honorine Kouto 20 , Assia Lamrani-Ghaouti 21 , Marie Bergeaud 21 , Stefan Michiels 3 , Sofia Rivera 3 1 Radiation oncology, Institut Godinot, Reims, France. 2 Biostatistics and Epidemiology, Gustave Roussy, Villejuif, France. 3 Radiation oncology, Gustave Roussy, Villejuif, France. 4 Radiation oncology, Institut Curie, Paris, France. 5 Radiation oncology, Centre Eugene Marquis, Rennes, France. 6 Radiation oncology, Institut de Cancérologie de Lorraine, Nancy, France. 7 Radiation oncology, Centre Léon Bérard, Lyon, France. 8 Radiation oncology, Centre Henry Becquerel, Rouen, France. 9 Radiation oncology, Hopital du Scorff, Lorient, France. 10 Radiation oncology, Institut du Cancer de Montpellier, Montpellier, France. 11 Radiation oncology, Centre Oscar Lambret, Lille, France. 12 Radiation oncology, Centre Georges-François Leclerc, Dijon, France. 13 Radiation oncology, Institut de Cancérologie de l'Ouest, Angers, France. 14 Radiation oncology, Institut Paoli Calmettes, Marseilles, France. 15 Radiation oncology, Institut Bergonié, Bordeaux, France. 16 Radiation oncology, Centre Jean Perrin, Clermont- Ferrand, France. 17 Radiation oncology, Centre Paul Strauss, Strasbourg, France. 18 Radiation oncology, Centre Antoine Lacassagne, Nice, France. 19 Radiation oncology and Henri Mondor Breast Center, GHU Henri Mondor, Créteil, France. 20 Radiation oncology, Centre Galilée - Hôpital Privé La Louvière, Lille, France. 21 Biostatistics and Epidemiology, Unicancer, Paris, France Purpose/Objective: Despite advances in radiotherapy and systemic treatments, some patients with breast cancer still develop locoregional or metastatic recurrences or a second primary malignancy. This pre-planned HypoG- 01 analysis aimed to describe recurrence patterns, assess dosimetric coverage, and identify associated clinical factors. Material/Methods: This descriptive analysis included the 1260 patients enrolled in the HypoG-01 trial. Only the first documented event up to September 2024 was considered, including locoregional recurrences (LRR), distant relapses, or second malignancy. Each
Conclusion: Locoregional recurrences were infrequent ( ≈ 2.1%) in HypoG-01 at 5 years, with most events being distant or second cancers. The overrepresentation of left-sided tumours among the LRR may be related to their proximity to the heart. All but one LRR were located inside the ESTRO CTV, supporting its reliability for regional nodal irradiation. References: Brion T, et al. Early toxicity of moderately hypofractionated radiation therapy in breast cancer patients receiving locoregional irradiation: First results of the UNICANCER HypoG-01 phase III trial. Radiotherapy and Oncology [Internet]. 2025 Jun 1 [cited 2025 Aug 6];207.Nantavithya C, et al. An improved method for analyzing and reporting patterns of in-field recurrence after stereotactic ablative
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