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

Abstract

Abstract BACKGROUND: Boost radiotherapy (B-RT) improves outcome in patients (pts) with invasive breast cancer. It's 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 women's 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<0.05). 46% were Estrogen Receptor positive (ER+), 30% B-RT and 16% noB-RT. 22% RE+ in B-RT take TMX vs 9.4 % RE+ noB-RT. Total LR 65 (10%). In situ LR 30 pts (4,6%) and Invasive (Inv) 35 (5,4%). By subgroup, LR in B-RT 47 (12%) vs. 18 (7%) in noB-RT. By subtype, In situ LR in B-RT 20 (5.1%) vs. noB-RT 10 (4%). Inv LR in B-RT 27 (6.9%) vs. noB-RT 8 (3.2%). In uni & multivariate analysis, tumour size, Re-Excision, and TMX, are significant LR risk factors (p<0.05). 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<0.001). When Dose is introduced in multivariate analysis model, TMX lost signification. Contralateral local recurrence (CLR) in 29 pts (7%). Second tumours 9 pts (NSD between subgroups). Global disease free survival (DFS) is 80.5%, 77% in B-RT vs. 85% in noB-RT. Four pts have a LR combined with CLR; 2 pts have a LR and a second tumor; 1 pt with CLR and second tumour; 1 pt a Inv regional recurrence; 1 pt mixosarcoma in ipsilateral breast and lung metastases. Deaths: 3 pts (0.5%) after an Inv LR; 3 pts (0.5%) after Inv CR; 20 pts other causes; 10 pts lost their FU. Median FU in B-RT subgroup was 9y vs. 8.3y in noB-RT. The maximum FU according LR in B-RT is 20.6y vs. 17.4y in noB-RT. RL is not significant according to Boost (K-M p=0.398). Median LR in situ or inv depending of B-RT vs. noB-RT shows NSD (p=0.663). 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, Moià M, Reyes V, Arenas M, Pedro A, Ballester R, García V, Sanjosé S, Cusidó M, Jimenez C, Macià M, Solé JM, Farrus B. Study of boost radiotherapy's 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.