Abstract P5-17-08: Study of boost radiotherapy's influence on local control in 646 pure ductal carcinoma in situ breast cancer with long-term follow-up

BACKGROUND: Boost radiotherapy (B-RT) improves outcome in patients (pts) with invasive breast cancer. It9s use in patients with pure ductal carcinoma in situ (DCIS) is unclear. There are two ongoing randomize trials, results are expected in ten years. Twelve retrospective observational studies have been published since 2006, the recent meta-analysis , support boost in the presence of positive margins. PATIENTS and METHODS: We analyse a retrospective women9s cohort of 646 pure DCIS patients (pts) treated mainly in two Hospitals (n=518) from 1993 to 2014. The other ten Hospitals included 128 pts all 2005 long. Proportions were compared by boost status, using the chi-square tests. The impact of boost radiation on the development of local recurrence (LR) was determined using survival analyses. In the comparison of Kaplan-Meier (K-M) was used log-rank test. RESULTS: B-RT subgroup is 394 pts (61%), noB-RT 252 (39%). Median follow-up (FU) is 8.8 years. High risk factors: young age, size, margin status and tamoxifen (TMX) show differences among B-RT (p . Boost total doses >16 Gy in the B-RT subgroup is a LR significant risk factor related to 10-16 Gy (p∼0.05) . TMX and Dose Boost are related (p CONCLUSIONS: In this large cohort retrospective study with long-term follow-up B-RT was associated with similar LR as noB-RT despite being used more frequently with higher risk disease. Dose boost >16 Gy has a protective effect. Tamoxifen and boost dose are related variables. Further evidence, based on ongoing randomized trials results is essential. Citation Format: Cambra MJ, Moreno F, Sanz X, Anglada L, Moia M, Reyes V, Arenas M, Pedro A, Ballester R, Garcia V, Sanjose S, Cusido M, Jimenez C, Macia M, Sole JM, Farrus B. Study of boost radiotherapy9s influence on local control in 646 pure ductal carcinoma in situ breast cancer with long-term follow-up. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-17-08.