Abstract P3-17-01: Long-term rates of breast preservation after breast-conserving therapy for ductal carcinoma in situ

Abstract

Abstract Background: Despite evidence that radiotherapy (RT) after breast-conserving surgery (BCS) for ductal carcinoma in situ (DCIS) halves the risk of recurrence, the benefit of RT in the management of DCIS continues to be a matter of controversy. One argument against the use of RT after BCS is that patients who develop ipsilateral local recurrence (LR) can be salvaged with further breast-conserving surgery such that the omission of RT will lead to high rates of breast preservation while minimizing exposure to RT. Breast preservation is an important determinant of quality of life for women with early stage breast cancer and DCIS. Yet the management of LR and the impact of RT on the resultant long-term risks of bilateral breast preservation in a population of women with DCIS are unclear. We assessed the treatment of LR, the impact of RT on the use of salvage mastectomy and the long-term risks of bilateral breast preservation achieved in a population of women with DCIS treated with BCS alone or BCS+RT. Methods: A population-based analysis of women diagnosed with DCIS from 1994-2003 treated with BCS alone or BCS+RT with pathology review. Treatment and outcomes, including the development of LR and contralateral breast events, were determined by administrative databases with validation by review of operative or pathology reports. Median follow-up was 10.2 years for cases treated by BCS alone, 11.6 years for those treated by BCS+RT. We used a propensity-adjusted Cox proportional hazards model to evaluate factors associated with the use of salvage mastectomy for LR and to evaluate factors associated with any mastectomy. We assessed the risk of long-term breast preservation by calculating the KM 10-year risk of ipsilateral mastectomy and any mastectomy. Results: The population cohort includes 3303 women with pure DCIS;1649 (50%) were treated by BCS alone, 1654 (50%) received BCS+RT. Women treated with RT had more high risk features of DCIS than those treated by BCS alone. LR developed in 343 (21%) women treated by BCS alone and in 257 (15.5%) women treated by BCS+RT (p<0.01). Most women who developed LR received salvage mastectomy, irrespective of age at diagnosis and histology. Salvage mastectomy was used in 57.4% (197/343) of cases that recurred after BCS alone and in 67.6% (173/257) that recurred after BCS+RT. The likelihood of receiving salvage mastectomy for LR was similar in patients initially treated by BCS+RT vs. those initially treated BCS alone. Most (90%) of mastectomies were performed for a LR. Overall, individuals initially treated by BCS+RT had a 29% lower probability of having a mastectomy at 10 years compared to those treated by BCS alone (HR=0.71, 95%CI: 0.60,0.84,p<0.0001). The 10 year mastectomy-free survival rates are 82.7% for women initially treated by BCS alone and 87.3% for those treated by BCS+RT (p=0.0096). Conclusion: Women who received RT after BCS for DCIS experience a greater likelihood of long-term bilateral breast preservation. This is attributable to the lower risks of LR and that most local recurrences after breast-conserving therapy are treated by salvage mastectomy. Long-term breast preservation should be considered in discussions weighing the benefits and risks of RT after conservative surgery for DCIS. Citation Format: Rakovitch E, Nofech-Mozes S, Hanna W, Gu S, Fong C, Tuck A, Sengupta S, Elavathil L, Jani P, Done S, Miller N, Youngson B, Bonin M, Chang M, Paszat L. Long-term rates of breast preservation after breast-conserving therapy for ductal carcinoma in situ [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-17-01.