Postoperative Re-irradiaTion With and Without HYPERthermia, or Surgery Only: Toxicity, Quality of Life and Survival in Patients With Locoregional Recurrent Breast Cancer

The optimal management of LRR breast cancer is multidisciplinary, and based on various prognostic risk factors and previous treatments. The surgical treatment of local recurrences is salvage mastectomy after previous breast-conserving therapy, or local excision after previous mastectomy. Regional treatment of tumor-positive lymph nodes consists of axillary radiotherapy and/or lymph node dissection. Intermediate- and high-risk LRR patients have an indication for surgery +/- postoperative irradiation to improve locoregional control and disease-free survival. In previously irradiated high-risk LRR patients, postoperative re-irradiation is administered with or without hyperthermia in the Netherlands depending on the treating center and treating professional. In unresectable LRR, primary re-irradiation with hyperthermia is the evidence-based standard of care in high-risk LRR in the Netherlands. Hyperthermia is used to increase the therapeutic efficacy of re-irradiation. The introduction of preoperative systemic therapy in 2010 resulted in more resectable high-risk LRRs. This resulted in an increased number of resectable LRR and indications for postoperative re-irradiation instead of primary re-irradiation, including variation in the use of hyperthermia. There is no evidence-based standard of care regarding the combination of postoperative re-irradiation with or without hyperthermia in high-risk LRR patients. The major problem is that only retrospective data and no prospective (randomized) data is available on oncological outcomes (survival and recurrence) and toxicity following postoperative re-irradiation and hyperthermia. Consequently, there is a high need to assess oncological outcomes and toxicity of postoperative re-irradiation with or without hyperthermia in a randomized controlled trial (RCT). So far, an RCT has not been feasible due to the large variation in postoperative re-irradiation and hyperthermia, and preferences regarding hyperthermia-treatment by professionals. In the RT-HYPE study, the investigators evaluate oncological outcomes, toxicity and quality of life in high-risk LRR patients, including the harmonization of hyperthermia-treatment. The results of the RT-HYPE study are needed for the optimization of the shared decision making (SDM) process on post-operative re-irradiation with or without hyperthermia, between professionals and patients. In addition, these results allow to set-up a future RCT comparing postoperative re-irradiation with and without hyperthermia treatment. During the inclusion of patients since February 2024, we have observed some variation in the treatment of high-risk LRRs between participating centers, which is a result of the SDM-process and variation in clinical practice. Consequently, in some patients postoperative re-irradiation +/- hyperthermia is omitted. Also, in patients with a local chest wall recurrence, surgery is sometimes omitted in case of an excellent response to NAST, limiting local treatment to re-irradiation (+/-hyperthermia) only. Consequently, both surgical and radiotherapy treatments vary in high risk LRR patients. In addition, recently published evidence in primary breast cancer showed that post-mastectomy and/or axillary radiotherapy is not needed in selected patients (SUPREMO, Kunkler et al. NEJM 2025, NSABP B-51/RTOG 1304 Mamounas et al. NEJM 2025). First, the randomized controlled SUPREMO trial evaluated the omission of post mastectomy radiotherapy (PMRT) in breast cancer patients with pT1 2N1, pT3N0, or pT2N0 with grade 3 +/- lymphovascular invasion, treated with mastectomy, axillary dissection and systemic therapy. The median follow-up was 9.6 years. Post-mastectomy radiotherapy did not increase 10-year overall survival (i.e. primary endpoint), which was 81.4% with PMRT and 81.9% without PMRT. Secondary outcomes including 10-yr local (1.1%+PMRT, 4.5% no PMRT) and locoregional recurrence rates (2.7%+PMRT, 4.5% no PMRT), disease-free survival (76.2%+PMRT, 75.5% no PMRT) and distant-metastasis free survival (78.2%+PMRT, 79.2% no PMRT) were comparable in both groups. Second, the randomized controlled NSABP B-51/RTOG 1304 trial evaluated postoperative axillary nodal irradiation (ax RT) in patients with clinical stage T1-3N1 and tumor negative axillary lymph nodes after neoadjuvant systemic therapy, (targeted) axillary dissection and local treatment (i.e. breast-conserving surgery and whole breast irradiation or mastectomy (and no PMRT)). After a median follow-up of 59.5 months, 5-year invasive breast cancer recurrence-free interval (i.e. primary endpoint) was 92.7 (+axillary RT) and 91.8% (no axillary RT). The secondary outcomes were similar in both groups, i.e. 5-yr locoregional recurrence-free (98.9% +ax RT, 98.4% no ax RT), distant recurrence-free survival (93.4%+ax RT), 93.4% no ax RT), disease-free survival (88.3% +ax RT, 88.5% no ax RT). Since the indication for postoperative re-irradiation in high-risk LRR is extrapolated from primary breast cancer, in the absence of evidence in the recurrent setting, it is likely that the group with high-risk LRR treated with surgery without postoperative re-irradiation +/- hyperthermia treatment, will increase. After discussion with the study team and radiation oncologists of participating centers in October 2025, we have decided to include two additional groups that reflect current clinical practice: 1. Patients with high-risk LRR (as described in Section Inclusion Criteria) who do not receive postoperative re-irradiation after salvage mastectomy. 2. Patients with a chest wall recurrence after previous mastectomy (as described in Section Inclusion Criteria) and a clinical/radiological complete response after NAST and treated with re-irradiation (+/- hyperthermia) for any microscopic disease without local excision.

• Quality of Life at 2 and 5 years after diagnosis of LRR disease [Time frame: at 2 and 5 years after diagnosis of LRR disease]
• Quality of Life at 2 and 5 years after diagnosis of LRR disease [Time frame: at 2 and 5 years after diagnosis of LRR disease]
• LRR-free survival in LRR patients [Time frame: at 2 and 5 years after diagnosis of LRR disease]
• distant metastasis-free survival in LRR patients [Time frame: at 2 and 5 years after diagnosis of LRR disease]
• breast-cancer event-free survival in LRR patients [Time frame: at 2 and 5 years after diagnosis of LRR disease]
• overall survival in LRR patients [Time frame: at 2 and 5 years after diagnosis of LRR disease]
• Referral patterns in patients diagnosed with LRR [Time frame: 5 year]