Abstract Book

S729

ESTRO 37

4 LMU Munich, Munich Cancer Registry MCR of the Munich Tumour Centre TZM at the Institute of Medical Information Processing- Biometry and Epidemiology IBE, Munich, Germany Purpose or Objective The objective of the present study was to evaluate the effectiveness of postoperative radiotherapy after breast conserving surgery (BCS) in DCIS in a large patient population treated in clinical practice. Material and Methods Data were provided by the population-based Munich Cancer Registry. Between 1998 and 2014, 1048 female patients with diagnosis of DCIS and treated at two Breast Care Centres were included in this observational study. The effectiveness of postoperative radiotherapy and variables predicting the use of radiotherapy were retrospectively analysed. Median follow-up was 85.5 After adjusting for age, tumour characteristics and therapies, Cox regression analysis for local recurrence- free survival identified RT as an independent predictor for improved local control (HR: 0.612; 95%CI: 0.399- 0.939, p=0.025). Ten-year cumulative incidence of in- breast recurrences was 14.6% following BCS, compared to 9.1% in patients receiving postoperative radiotherapy (p=0.017). As an estimate for disease-specific survival, 10-year relative survival was 105.4% for patients receiving postoperative radiotherapy and 101.6% without radiotherapy. On multivariate analysis, postoperative radiotherapy was not associated with improved overall survival (HR 0.526; 95%CI: 0.263-1.052, p=0.069). Over time, a significant increase of RT was registered: while 1998 only 42.9% of patients received postoperative radiotherapy, the proportion rose to 91.2% in 2014. Women aged <50 years (OR: 1.616, 95%CI: 1.054-2.477, p=0.004) or with negative hormone receptor status (OR: 2.124, 95%CI: 1.305-3.457, p=0.002) were more likely to receive postoperative radiotherapy after BCS. Conclusion In conclusion, this study provides insights regarding the adoption and treatment pattern of postoperative RT following BCS for DCIS in a large cohort reflecting "real- life" clinical practice in this setting. Postoperative RT was found to be associated with a reduced risk of ipsilateral recurrence and no survival benefit compared to observation alone. EP-1332 Efficacy of an accelerated hypofractionted schedule for whole breast and regional node irradiation A. Montero Luis 1 , M. Hernandez 2 , R. Ciervide 1 , M. Garcia- Aranda 1 , B. Alvarez 1 , J. Valero 1 , A. Acosta 1 , R. Alonso 1 , M. Lopez 1 , E. Sanchez 1 , O. Hernando 1 , C. Rubio 1 1 Hospital Universitario Madrid Sanchinarro - Grupo Hospital de Madrid, Radiation Oncology, Madrid, Spain 2 University Hospital Rey Juan Carlos, Radiation Oncology, Madrid, Spain Purpose or Objective Regional nodal irradiation (RNI) in node-positive women with breast cancer is indicated to improve loco-regional control and survival. Hypofractionated whole breast radiotherapy appears as a standard treatment, although there is still controversy about its use for regional nodal irradiation. We present our results in terms of acute toxicity and local control of RNI with a hypofractionated accelerated radiotherapy schedule. Material and Methods From January-2015 to December-2016, 140 patients with a median age of 50 years (range 31-84) were treated according to our institution hypofractionated radiotherapy schedule. Clinical staging (AJCC): 5p (3.6%) stage 0; 31p (22.1%) stage IA; 39p (27.9%) stage IIA; 43p months. Results

(30.7%) stage IIB; 15p (10.7%) stage IIIA; 5p (3.6%) stage IIIB and 2p (1.4%) stage IV. All patients underwent breast surgery, both conservative tumorectomy (63p, 45%) or mastectomy (77p, 55%). Ninety-eight patients (70%) underwent complete axillary lymph node dissection (ALND) whereas 42p (30%) underwent selective sentinel lymph node biopsy exclusive. Histology: 115p (82.17%) infiltrating ductal carcinoma, 20p (14.3%) infiltrating lobular carcinoma and 5p (3.6%) ductal carcinoma in-situ. Molecular subtypes: Luminal A 48p (34.3%), Luminal B 54p (38.6%), Her2-enriched 16p (11.4%) and triple-negative 22p (15.7%). Radiotherapy comprises the whole breast or chest wall and the regional nodes levels I-IV up to a total dose of 40.5Gy@2.7Gy/day. In 12p (8.6%) irradiation of internal mammary chain was considered according to pN2-3 axillary affectation or tumors of central-inner quadrants. Simultaneous integrated boost (SIB) was administered to all patients after BCS and to 3 patients with close/focally affected margins after mastectomy, total dose of 48Gy@3.2Gy/day in 62p and 51Gy@3.4 Gy/day in 4p. Systemic therapy: 116p (82.9%) received chemotherapy either neoadjuvant (51p, 36.4%) or adjuvant (65p, 46.4%); 108p (77.1%) hormone therapy (tamoxifen 52p, aromatase inhibitors 56p) Results With a median follow-up of 22.5 months (range 5-33), 1p (0.7%) presented local relapse, 3p (2.1%) regional nodal relapse and 4p (2.9%) distant metastases including the 2p that presented stage IV at diagnoses. At date of last follow-up, 136p (97.1%) are alive without tumor, 3p (2.1%) alive with tumor and 1p (0.7%) has died because of breast cancer. Actuarial 3-year locoregional free survival (LRFS), disease free survival (DFS) and overall survival (OS) were 89.9%, 87.3% and 99% respectively. Acute toxicity was null or mild. Nearly all patients (135p, 96.4%) experienced skin toxicity: grade 1 = 89p (63.6%), grade 2 = 43p (30.7%) and grade 3 = 3p (2.1%). Other toxicities: arm lymphedema in 8p (5.7%): grade 1 = 6p (4.3%) and grade 2 = 2p (1.4%); acute pneumonitis in 2p (1.4%), both grade 1. Conclusion Hypofractionated schedules for whole breast and RNI is feasible and well tolerated. Longer follow-up is needed to address the observed outcomes. C. De la Pinta Alonso 1 , E. Fernández-Lizarbe 1 , A. Muriel 2 , B. Pérez Mies 3 , R. Hernanz De Lucas 1 , M. Martín Sánchez 1 , A. Montero Luis 4 , S. Sancho García 1 1 Hospital Ramon y Cajal, Radiation Oncology, Madrid, Spain 2 Hospital Ramon y Cajal, Statistical Department, Madrid, Spain 3 Hospital Ramon y Cajal, Pathological Department, Madrid, Spain 4 HM Madrid, Radiation Oncology, Madrid, Spain Purpose or Objective Mastectomy without radiotherapy is the standard of care in our institution for high-risk patients in Van Nuys Prognostic Index (VNPI) classification in Ductal carcinoma in situ (DCIS). The aim of this study is to identify predictive factors for tumour recurrence in this group of patients. Material and Methods From 2000 to 2014, 174 patients with DCIS treated by mastectomy were retrospectively studied. Tumor characteristics and treatment-factors were tested for influence on tumor recurrence. We analyzed overall survival (OS EP-1333 Predictive Factors of Recurrence after Mastectomy for Ductal Carcinoma in situ