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2010). In early stage breast cancer, their presence is associated at higher risk of death, distant relapse and locoregional relapses. In that context, the purpose of this study is to evaluate if whether DTC presence would be a predictive factor for the benefit of comprehensive locoregional irradiation on locoregional relapse at long term. Material and Methods Patients with localized breast cancer were eligible for this prospective cohort after informed written consent. DTC was obtained from a medullary iliac crest sample performed at time of surgery or prior to any primary systemic therapy and DTC status was prospectively assessed by trained pathologists after immunocytostaining. Irradiation volumes (breast or chest wall +/- boost +/- regional lymph nodes: internal mammary nodes & supraclavicular nodes (IMN/SCN) +/- axillary nodes) were defined per standard of care. Locoregional relapse was defined as documented ipsilateral invasive relapse occurring in the breast, chest wall and/or in regional lymph nodes, prior to any distant metastatic relapse. Cumulative incidence rates and hazard ratio were obtained using both Cox and Fine-Gray models, taking into account metastatic relapse and death as competitive events. Interaction tests were performed to confirm the predictive value of DTC status in a multivariate analysis. Results From November 1998 to September 2005, a total of 620 patients with localized breast cancer was included. Overall, 94 patients (15.2%) were DTC-positive. After a median FU of 11.7 years, 47 patients (7.6%) experienced a locoregional relapse. Of these patients, 14 were initially DTC-positive (n=14/94, 15%) and 33 were DTC- negative (n=33/526, 6%). DTC detection was associated with a higher risk of locoregional relapse in univariate and mul tivariate analyses (Cox, HR=3.26, 95%CI=[1.58;5.74], p=0.001). In the multivariate subgroup analysis, IMN/SCN irradiation significantly reduced locoregional relapse for DT C- positive patients comparing to DTC-negative patients (interaction test: HR=0.3, 95%CI=[1.51;5.27], p=0.003). DTC status was a predictive marker for the efficacy of IMN/SCN irradiation for local control. Importantly, IMN/SCN was the only irradiation volume with a impact on locoregional relapse in patients, according to their DTC status, and the predictive value of DTC status for the benefit of locoregional irradiation was independent of the locoregional nodal (pN) status. Conclusion This long term analysis confirms the independent long- term prognostic value of DTC for locoregional relapse in early stage breast cancer. Moreover, IMN/SCN irradiation decreases the risk of locoregional relapse in DTC-positive patients. After further studies, DTC status could be a decision tool to better tailor adjuvant radiation therapy in early stage breast cancer patients. OC-0160 DCIS treated with breast conservative surgery and radiotherapy: a national multicentre experience I. Meattini 1 , N. Pasinetti 2 , B. Meduri 3 , F. De Rose 4 , M.C. De Santis 5 , V. Lancellotta 6 , F. Rossi 7 , P. Franco 8 , F. Alongi 9 , C. Saieva 10 , E. Olmetto 1 , I. Desideri 1 , E. D'Angelo 3 , L. Triggiani 2 , U. Ricardi 8 , P. Bastiani 7 , C. Aristei 6 , L. Lozza 5 , M. Scorsetti 4 , L. Livi 1 1 Azienda Ospedaliero Universitaria Careggi - University of Florence, Radiation Oncology Unit - Oncology Department, Florence, Italy 2 Brescia University, Radiation Oncology Unit, Brescia, Italy 3 University Hospital of Modena, Radiation Oncology Unit, Modena, Italy

Results MBC (74.1%), MedBC (60.6%), ACC (75.7%), and EBC (28.7%) had significantly higher proportions of TNBC compared to IDC (14.0%), while ILC (1.8%) had significantly lower proportion of TNBC (p<0.001). TNBC predicted a lower OS in IDC (p<0.001), EBC (p<0.001), and ILC (p<0.001), but had no prognostic significance for pts with MBC (p=0.261), MedBC (p=0.142), or ACC (p=0.504). Overall, 50% of pts underwent lumpectomy, 50% underwent mastectomy, most pts received chemotherapy (78.7%), and over half (58.7%) received radiotherapy (RT). However, treatment characteristics did vary by histology. Mastectomy was more common in MBC (58.1%), ILC (64.7%), and EBC (58.2%), and less common in MedBC (39.2%) and ACC (29.4%), when compared to IDC (49.7%, p<0.001). When compared to IDC (58.7%), pts with MBC received RT less often (51.9%, p<0.001), and pts with ILC were treated with RT more often (64.3%, p<0.001). Among pts with TNBC, EBC, ILC, and MBC were associated with inferior OS compared to IDC (p<0.001), while ACC and MedBC were associated with superior OS (p<0.001). MVA identified unique patterns of prognostic factors that varied by histology. The absence of RT was a predictor of OS only in IDC (HR 1.14, p=0.001) and in MBC (HR 1.07, p=0.023), and the absence of chemotherapy was a predictor of OS only in IDC (HR 1.94, p<0.001) and in MedBC (HR 3.34, p=0.024). Conclusion Our results indicate that the histologic heterogeneity in TNBC significantly informs patient outcomes when compared to IDC, and thus, has the potential to aid in the development of optimum personalized treatments. OC-0159 Disseminated tumor cells as factor of benefit of regional lymph nodes irradiation in breast cancer F. Mignot 1 , F.C. Bidard 2 , S. Dureau 3 , A. Fourquet 1 , F. Berger 3 , D. Loirat 2 , C. Proudhon 2 , A. Vincent-Salomon 4 , J.Y. Pierga 2 , Y. Kirova 1 1 Institut Curie, Département de Radiothérapie, Paris, France 2 Institut Curie, Département d'Oncologie médicale, Paris, France 3 Institut Curie, Département de Statistique, Paris, France 4 Institut Curie, Département d'Anatomie et Cytopathologie, Paris, France Purpose or Objective The disseminated tumor cells (DTC) are collected in the bone marrow and are the witness of micrometastatic spread (patients cM0(i+) - Breast cancer TNM staging,