Abstract P2-12-02: Is breast-conserving therapy effective in women with large ductal carcinoma in situ (DCIS) lesions? A population-based analysis

Abstract

Abstract Background: Most women diagnosed with DCIS will be treated by breast-conserving surgery (BCS) with or without radiotherapy (RT). Data on outcomes following breast-conserving therapy are predominantly based on women with small (<25mm) lesions. The paucity of data on outcomes of women with larger (>40mm) DCIS lesions leads to uncertainty of the appropriateness of breast-conserving therapy for women with larger lesions. Specifically, it is unclear if women with large tumors experience higher risks of local recurrence (LR) and invasive LR after BCS+/-RT that would preclude recommendations of breast-conserving therapy. We report the outcomes and evaluate the impact of large tumor size (>40mm) on recurrence risk in a population of women with pure DCIS treated by BCS alone or with RT. Methods: The cohort includes all women diagnosed with DCIS in Ontario from 1994-2003 treated with BCS +/- RT; 82% had pathology review. Treatment and outcomes were ascertained through administrative databases and validated by chart review. Cox proportional hazards model was used to evaluate the impact of tumor size (≤10mm,11-25mm, 26-39mm, ≥40mm) on the development of any LR (DCIS or invasive) and invasive LR. The 10 and 15-year LR-free survival (LRFS) and invasive LRFS rates were calculated using the Kaplan-Meier method with differences compared using the log-rank test. Results: The cohort includes 3262 women with DCIS treated by BCS (N=1635 had RT). Median age at diagnosis was 59 years (IQR 50-68 years). Median follow-up was 13 years (IQR 8-15 years). Distribution of tumor size: 707 (22%) ≤10mm, 524 (16%) 11-25mm, 107 (3%) 26-39mm, 84 (3%) ≥40mm, unable to determine in 1840 (56%). Women with lesions ≥ 40mm were more likely to be ≤50 years of age at diagnosis (p=.02), have high nuclear grade (p<.001), multifocality (p<.001), and positive margins (p<.001) compared to women with smaller lesions. On multivariable analyses adjusted for age and year of diagnosis, tumor size ≥40mm was significantly associated with an increased risk of LR compared to size ≤10mm (HR=2.5, 95%CI:1.64-3.81). Other factors associated with LR were age <50 years (p<.001), omission of RT (p<.001), high nuclear grade (p=.002), and multifocality (p=.0008). Tumor size ≥40mm was not significantly associated with an increased risk of invasive LR (HR=1.68, 95%CI:.94-3.04). Women with tumour size ≥40mm treated with BCS alone had lower 10 and 15 year LRFS (53% and 41%) and invasive LRFS rates (78% and 75%) compared to women with smaller lesions. However, women with larger lesions treated with RT had significantly higher LRFS and invasive LRFS rates Outcomes by tumour size for women with DCIS treated with BCS with or without RT ≤10mm N=70711-25mm N=52426-39mm N=107≥40mm N=84p-valueBCS AloneLRFS (%) 10 yr85797053<0.001 15 yr81746741 Invasive LRFS (%) 10 yr928786780.03 15 yr89838375 BCS + RTLRFS (%) 10 yr928874850.01 15 yr86847079 Invasive LRFS (%) 10 yr959492910.27 15 yr90918789 . There was a significant interaction between tumor size ≥40mm and RT (p=.02). Conclusions: Women with DCIS lesions ≥40mm treated by BCS alone experience significantly higher risks of LR and invasive LR compared to smaller lesions but this risk can be mitigated with the addition of RT. Citation Format: Lalani N, Paszat L, Nofech-Mozes S, Sutradhar R, Gu S, Hanna W, Fong C, Miller N, Youngson B, Done SJ, Tuck A, Chang MC, Sengupta S, Jani PA, Bonin M, Rakovitch E. Is breast-conserving therapy effective in women with large ductal carcinoma in situ (DCIS) lesions? A population-based analysis [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-12-02.