ESTRO 2021 Abstract Book

S912

ESTRO 2021

minimizes the delay of surgery or chemotherapy. Recent trials show that 5 fractions results in lower acute toxicity with similar late toxicity, and importantly without a higher risk for relapse. Theoretically, NART in 5 fractions could result in a shorter overall treatment time since the waiting time between surgery/chemotherapy and RT is omitted. This pilot trial is the first to report on accelerated NART in 5 fractions with simultaneously integrated boost (SIB), and the first analysis focusses on the difference in OTT with adjuvant RT. Future analyses will focus on pathological complete response rate, mastectomy rate and Twenty patients eligible for neo-adjuvant chemotherapy (NACT) and breast conserving surgery, according to multidisciplinary decision, were randomized between NART followed by NACT and surgery (intervention group) or NACT followed by surgery and RT (control group). Figure 1 gives an overview of both treatment arms. In both arms, RT treatment was given to the whole breast in 5 fractions of 5.7Gy with a SIB of 6.2Gy per fraction, in prone position. When lymph nodes were involved, 5 fractions of 5.4Gy were given to the regional lymph nodes and the patient was positioned in supine position. In the intervention group, the time from diagnosis to surgery (OTT) and the time between diagnosis and chemotherapy (NACT-delay) were calculated. In the control group, the time from diagnosis to the last RT-fraction was calculated (OTT). The analysis was done on an intention-to-treat (ITT) basis using a two-sided student T-test with a significance level of p<0.05. surgery complications. Materials and Methods

The study was powered to detect a 14 day difference in OTT between both groups. Figure 1 Schematic overview of the time schedule in both treatment arms

Results Of the 20 patients included, 19 patients were analyzed in the ITT analysis, since one patient (without lymph node involvement) in the control group did not receive RT due to progression during NACT followed by a mastectomy. One patient randomized to NART did not receive the treatment due to uncertainty over lymph node involvement during staging investigations. OTT was significantly shorter in the intervention group (mean 211 days, range 196 – 229) compared to the control group (mean 237, range 211 – 268, p=0.001). The difference in mean duration from diagnosis to the first dose of NACT was a non-significant 3 days longer (30 vs 27 days, p=0.28). Conclusion NART before NACT resulted in a shorter OTT due to the elimination of waiting time between surgery and adjuvant RT. PO-1096 Safety of concurrent TDM-1 and radiotherapy for patients with residual HER2-positive breast cancer C. Becherini 1 , G. Stocchi 1 , L. Visani 1 , M.C. De Santis 2 , R.R. Colciago 2 , S. Pedretti 3 , S.M. Magrini 3 , M. Nuzzo 4 , D. Genovesi 4 , L.A. Ursini 4 , A. Bonanni 5 , E. Ippolito 6 , S. Ramella 6 , F. De Renzi 7 , A. Fontana 8 , P. Vitucci 9 , L. Angelini 1 , C. Orsatti 1 , I. Desideri 1 , V. Scotti 1 , L. Orzalesi 10 , M. Bernini 10 , L. Sanchez 10 , J. Nori 11 , S. Bianchi 12 , I. Meattini 1 , L. Livi 1 1 University of Florence, Department of Experimental and Clinical Biomedical Sciences, Florence, Italy; 2 Istituto Nazionale dei Tumori, Radiation Oncology Unit, Milan, Italy; 3 Spedali Civili di Brescia, Radiotherapy Unit, Brescia, Italy; 4 SS. Annunziata Hospital, Radiotherapy Unit, Chieti, Italy; 5 Fatebenefratelli Hospital, Radiotherapy Unit, Rome, Italy; 6 Campus-Biomedico University, Radiation Oncology Unit, Rome, Italy; 7 San Martino Hospital, Radiotherapy Unit, Belluno, Italy; 8 Santa Maria Goretti Hospital, Radiotherapy Unit, Latina, Italy; 9 Pugliese Ciaccio Hospital, Radiotherapy Unit, Catanzaro, Italy; 10 Azienda Ospedaliero-Universitaria Careggi, Breast Surgery Unit, Florence, Italy; 11 Azienda Ospedaliero-Universitaria Careggi, Diagnostic Senology Unit, Florence, Italy; 12 Azienda Ospedaliero-Universitaria Careggi, Pathology Unit, Florence, Italy Purpose or Objective Patients with HER2-positive early breast cancer with residual invasive disease after primary systemic therapy (PST) have a higher risk of recurrence and death than those achieving pathologic complete response (pCR). In the phase III KATHERINE study, adjuvant Trastuzumab Emtansine (TDM-1) reduced the risk of recurrence or death by 50% compared with trastuzumab prosecution in this population. A recently presented subgroup analysis by Loibl et al showed an increase in grade ≥3 adverse events in the TDM-1 arm in patients treated with adjuvant radiotherapy as compared to patients not receiving radiotherapy (27.4% vs 16.4%) or patients treated with trastuzumab with or without radiotherapy (15.6% vs 14.6%). Our aim was to evaluate the acute side effects of TDM-1 administered concurrently with adjuvant radiotherapy in a real life multicentric register. Materials and Methods We retrospectively evaluated data of patients treated between January 2019 and December 2020 with concurrent TDM-1 and radiotherapy in adjuvant setting. Left ventricular ejection fraction (LVEF) was assessed at baseline, before and after radiotherapy. All toxicities were evaluated and scored using Common Terminology Criteria of Adverse Events (CTCAE) version 5.0. Results A total of 25 women treated in 7 Italian institutions were included in the analysis. Baseline patients’ characteristics are summarized in Table 1. In the acute setting, G1-2 dermatitis was recorded in 20 patients