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Background: Current trends in breast cancer treatment include the use of less aggressive surgeries to reduce morbidity, shorten hospital stays and improve cosmetic results. The aim of the study is to assess tumor cell viability after percutaneous ultrasound (US)-guided radiofrequency ablation (RFA) for small breast cancer by a combination of staining techniques. Methods: A prospective study was conducted at a single institution from 2013 to 2017. Twenty women with invasive ductal carcinoma of the breast measuring ≤ 20 mm were treated with US-guided RFA followed immediately by surgical resection. Tumor viability pre- and post-RFA was assessed with Hematoxylin and Eosin (H&E), Nicotinamide adenine dinucleotide (NADH), Succinate dehydrogenase (SDH), Cytochrome c oxidase (COX), Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and Cytokeratin 18 and 19 (CK18/CK19) staining techniques. Outcomes and correlation with the different techniques were evaluated with principal component analysis Cronbach’s alpha. Results: Oxidative enzymes in frozen sections showed loss of SDH and NADH in 13 of the 16 tumors (81%) and COX in 11 of the 13 tumors (84%). In paraffin-embedded tissues, CK18 was negative or markedly reduced in 98% and CK19 in 100% of the cases. Lack of evidence of cell death was seen in 3 cases where the maximum temperature achieved at the center of the tumor was ≤ 70ºC. The reliability and internal consistency between the different staining techniques was high (Cronbach’s alpha, 0.8), with concordance between the staining results of the oxidative enzymes and of CK18/CK19. Conclusion: Loss of tumor viability in small breast tumors after US-guided percutaneous RFA could be assessed in our series with different staining methods. CK18 and CK19 could be used in paraffin-embedded tissues as surrogate markers of tumor cell viability after immediate RFA.

IntroductionBreast cancer surgery currently focuses on de-escalating treatment without compromising patient survival. Axillary radiotherapy (ART) now replaces axillary lymph node dissection (ALND) in patients with limited sentinel lymph node (SLN) involvement during the primary surgery, and this has significantly reduced the incidence of lymphedema without worsening the prognosis. However, patients treated with neoadjuvant systemic treatment (NST) cannot benefit from this option despite the low incidence of residual disease in the armpit in most cases. Data regarding the use of radiotherapy instead of ALND in this population are lacking. This study will assess whether ART is non-inferior to ALND in terms of recurrence and overall survival in patients with positive SLN after NST, including whether it reduces surgery-related adverse effects.Methods and analysesThis multicenter, randomized, open-label, phase 3 trial will enroll 1660 patients with breast cancer and positive SLNs following NST in approximately 50 Spanish centers over 3 years. Patients will be stratified by NST regimen and nodal involvement (isolated tumoral cells or micrometastasis versus macrometastasis) and randomly assigned 1:1 to ART without ALND (study arm) or ALND alone (control arm). Level 3 and supraclavicular radiotherapy will be added in both arms. The primary outcome is the 5-year axillary recurrence determined by clinical and radiological examination. The secondary outcomes include lymphedema or arm dysfunction, quality of life based (EORTC QLQ-C30 and QLQ-BR23 questionnaires), disease-free survival, and overall survival.DiscussionThis study aims to provide data to confirm the efficacy and safety of ART over ALND in patients with a positive SLN after NST, together with the impact on morbidity.Ethics and disseminationThe Research Ethics Committee of Bellvitge University Hospital approved this trial (Protocol Record PR148/21, version 3, 1/2/2022) and all patients must provide written informed consent. The involvement of around 50 centers across Spain will facilitate the dissemination of our results.Trial registrationClinicalTrials.gov, identifier number NCT04889924.