ESTRO 36 Abstract Book

S342 ESTRO 36 _______________________________________________________________________________________________

evaluate failure patterns between the latter and HER2- enriched breast cancer after adjuvant PORT. Material and Methods Medical records of 516 women diagnosed with luminal B or HER2-enriched breast cancer that underwent surgical resection and PORT at Seoul National University Bundang Hospital (SNUBH) from 2003 to 2012 were retrospectively reviewed. Based on available IHC and FISH results, molecular subtypes were defined according to the 2013 St. Gallen International Expert Consensus recommendation as LB HER2- in 258 patients (50.5%), LB HER2+ in 136 patients (26.4%), and HER2-enriched in 122 patients (23.6%). Results Significant differences were observed between the luminal B subgroups, with LB HER2- demonstrating higher proportions of patients with age younger than 50 years (p=0.012), high histologic grade (p < 0.001), and positive expression of p53 (p=0.007). Patterns of care were also significantly different, with higher rates of systemic therapy omission in LB HER2- patients (p=0.001). After a median follow-up duration of 6.3 years, 10-year OS rates were 87.9% and 97.0% for LB HER2- and LB HER2+ , respectively (p=0.062). On multivariable Cox regression analysis, N stage in LB HER2- and N stage and histologic grade in LB HER2+ were identified as independent prognostic factors for relapse within 5 years. When compared with HER2- enriched breast cancer, LB HER2+ expressed lower rates of local recurrence (p=0.046) and brain metastasis (p=0.026). Conclusion Luminal B breast cancer manifest various patterns of failure among which trends to poorer prognosis is seen in the LB HER2- subgroup. The majority of LB HER2+ patients undergo some form of systemic treatment and demonstrate relatively better clinical outcomes than LB HER2- patients . Further stratification of risk prediction, particularly in the LB HER2- subgroup, and more aggressive systemic treatment are needed to improve treatment outcomes, of which p53 may be a potential marker. PO-0655 Patterns of locorégional failure in women with breast cancer treated by Postmastectomy Radiotherapy G. Loganadane 1 , Z. Xi 1 , N. Grellier Adedjouma 1 , H.P. Xu 1 , s. Krhili 1 , A. Chilles 1 , F. Campana 1 , A. Fourquet 1 , Y.Kirova 1 1 Institut Curie, Radiation oncology, Paris, France Purpose or Objective At Institut Curie, PMERT(Postmastectomy Electron Beam Radiation Therapy ) is the technique of choice to treat the chest wall for more than 30 years in women with breast cancer because it provides equivalent efficacy but decreases doses delivered to the organs at risk. Material and Methods From 964 patients with non-metastatic breast cancer treated with this technique between 2007 and 2011 at Institut Curie, data was available for 796 patients. With median follow-up of 64.1 months, locoregional relapse free survival at 5 years, metastases free survival at 5 years and overall survival at 5 years was 90% (IC95%: 88.1-92.4), 83,3% (IC 95% = [80,6 ; 86]) and 90.9% (IC95%: 88.9-93) respectively. Twenty three patients (2.9%) presented locoregional recurrences. The purpose of this study was to analyze the tumor characteristics and the radiation volumes/doses that could have resulted in failures. Mapping patterns of regional recurrences was also performed. Results The 23 patients that presented locoregional recurrence had mostly aggressive biologic features: grade III (modified Bloom–Richardson–Elston grading) in 17 patients (74%), high mitotic index in 16 patients (70%) and triple negative status in 12 patients (52%). Vascular embolism was present in 11 cases (48%). There were 4 cT1, 11cT2, 1cT3 and 6cT4. The overall positive nodes found in the lymphadenectomy were p33N+/111N and yp80N+/151N in patients without and with neoadjuvant chemotherapy.

The median age at recurrence was 59. The median locoregional relapse free survival and median overall survival was 28.3 months and 42.8 months respectively. Local recurrence (chest wall) occurred in 12 cases (56%) and infield regional recurrence was observed in 3 cases although sufficient dose was delivered. Marginal or outfield nodal recurrences were seen in 12 cases (56%) and involved level I or II in 9 cases. Interestingly, 3 axillary nodal recurrences occurred outside the ESTRO defined clinical target volumes. Synchronous and metachronous distant metastases were found in 14 and 4 patients respectively. Conclusion In our series, the local recurrence resulted mostly from of biologic radioresistance whereas regional recurrences were caused by geographical miss. Further follow-up and careful registration of the recurrencies is needed to improve the results PO-0656 Reirradiation+hyperthermia after surgery for recurrent breast cancer: 70% 5-year local control S. Oldenborg 1 , J. Crezee 1 , Y. Kusumanto 1 , R. Van Os 1 , S. Oei 2 , J. Venselaar 2 , P. Zum Vörde Sive Vörding 1 , C. Rasch 1 , T. Van Tienhoven 1 1 Academic Medical Center, Radiation Oncology Hyperthermia, Amsterdam, The Netherlands 2 Institute Verbeeten, Radiation Oncology, Tilburg, The Netherlands Purpose or Objective Combining reirradiation (reRT) with hyperthermia (HT) has shown to be of high therapeutic value for patients with inoperable locoregional recurrent breast cancer. The purpose of this study was to analyse the therapeutic effect and toxicity of reRT+HT following surgery of locoregional recurrent breast cancer in previously irradiated area. Material and Methods Two hundred and twenty-five patients were treated with re-RT+HT from 1982 till 2006. All patients received previous high dose radiation (median dose 50Gy with or without boost), overlapping with the current reRT field. Forty-two percent of the patients were treated for previous episodes of locoregional recurrent disease using either surgery, radiation, systemic therapy, or a combination of treatment modalities. At start of reRT+HT there was no macroscopically detectable recurrence after salvage mastectomy, chest wall resection, or local excision in 48%, 6%, and 46% of patients, respectively. ReRT consisted typically of 8x4Gy, twice a week or 12x3Gy, four times a week. Superficial hyperthermia was applied once or twice a week using 434MHz Contact Flexible Microstrip Applicators (CMFA), heating the tumor area to 41-43˚C for one hour. Results The treatment was well tolerated; only 3 patients did not complete treatment as planned due to herpes zoster infection, toxicity and refusal. Median follow-up time was 56 months. The 5-year infield local control (figure 1) and overall survival rates were 70% and 60%, respectively. A longer time interval to current recurrence, concurrent endocrine treatment, breast recurrences compared to chest wall recurrences and smaller recurrence sizes before treatment had a significantly positive effect on the duration of local control in multivariable analyses. Acute ≥ grade 3 toxicity occurred in 10% of patients. The risk of late ≥ grade 3 toxicity was 28% after 5 years and consisted mostly of ulceration (33%). In multivariable analyses the risk of overall late ≥ grade 3 toxicity was 4.6 times higher for patients treated with 4Gy fractions and abutted photon-electron fields (P = 0.032). Figure 1. Local control including confidence interval