Locoregional recurrence risk for women with various molecular subtypes of breast cancer treated with multicatheter interstitial accelerated partial-breast irradiation: Results from Pooled Registry of Multicatheter Interstitial Sites (PROMIS).

Abstract

73 Background: This study was performed to determine in breast tumor recurrence (IBTR) and regional nodal recurrence (RNR) rates for women with different subtypes of invasive ductal breast cancer treated with multicatheter interstitial accelerated partial breast irradiation (mAPBI). Methods: Data from 5 institutions was collected for patients treated from 1992-2013. We report the outcomes of 821 women with 830 breast cancers, all with ≥ 1 year of follow-up after completion of mAPBI. Molecular subtype analysis was performed for 582 women in whom ER, PR, Her-2, and grade were known. The Kaplan-Meier method was used to calculate overall survival (OS), IBTR and RNR. A univariate proportional hazard model was performed to estimate the risk of IBTR based upon molecular subtype, age, grade, N-stage, T-stage, margin status, tumor size, dose rate, endocrine therapy, and chemotherapy. Results: The median age of our patient cohort was 60 years. 50.0% (n = 415) of women had luminal A, 6.9% (n = 57) luminal B, 5.7% (n = 47) luminal Her-2, 1.8% (n = 15) Her-2, and 5.8% (n = 48) triple negative breast cancer (TNBC); an additional 29.8% (n = 248) could not be subtyped. With a median follow-up time of 6.5 years, the 5-year OS of our patient cohort was 94.8%. The 5-year IBTR was 3.5% for luminal A, 4.1% for luminal B, 5.1% for luminal Her-2, 13.3% for Her-2, 11.3% for TNBC, and 1.7% for non-subtyped women. Positive surgical margins and high grade correlated with risk for IBTR; molecular subtype and other variables did not. The 5-year RNR rates were 0.3% for luminal A, 4.6% for luminal B, 2.6% for luminal Her-2, 34.5% for Her-2, and 2.3% for TNBC. RNR risk was significantly higher for women with Her-2 compared to the other 4 subtypes. In addition, risk of RNR was significantly higher for women with luminal B compared to those of luminal A. Conclusions: Women with Her-2 and luminal B breast cancer may have higher RNR but not IBTR risk after mAPBI, as compared with women with luminal A subtype. Further follow-up, correlation with use of trastuzumab, and comparison of outcomes with whole breast irradiation will be valuable.