Abstract P2-13-03: Variation in the use of mastectomy (MAST) in women with small node negative breast cancer (BC) treated at US academic institutions
Authors: Vaz Luis Ines , Hughes Melissa E , Cronin Angel , Rugo Hope S , Edge Stephen B , Moy Beverly , Theriault Richard , Hassett Michael J , Winer Eric P , Lin Nancy U 
Published: May 2015

Abstract
Background: More than two decades ago several trials have shown equivalent survival between breast conserving surgery (BCS) and MAST. Among a contemporary cohort of patients (pts) with Stage I BC who would be expected to be candidates for BCS; we examined the initial choice of surgery and factors associated with it.
Pts and methods: Prospective cohort study including pts with clinical Stage I BC treated at a National Comprehensive Cancer Network center that participated in the BC outcomes database from 2000-09. Descriptive analyses were performed examining the proportion of pts who initially underwent MAST vs BCS. Factors associated with initial surgery were analyzed using multivariable logistic regression.
Results: Of 10,249 pts with clinical Stage I BC, 2,361(23%) underwent MAST as the initial surgery and 7,888 (77%) BCS. Of those, 8% were ultimately converted to MAST. The median time from diagnosis to initial surgery was longer among the MAST group (4 vs. 6 weeks).
Patient, tumor, care and institutional factors were associated with higher rates of initial MAST: 30% of pts with &lt;50 years of age had a MAST vs. 17% of those ≥70; 41% of pts with body mass index (BMI) &lt; 18.5 kg/m2 (underweight) had a MAST vs. 20% of those with a BMI &gt;30 kg/m2 (obese). There was significant institutional variation, with rates of initial MAST ranging from 14-30%. The use of preoperative magnetic resonance imaging (MRI) was associated with a higher rate of initial MAST (32% vs.22%). Differences by tumor subtype were observed, 38% of pts with HER2+/HR- tumors had initial MAST vs. 22-28% among other subtypes. In the multivariate model, age, BMI, comorbidity, income, center, stage, tumor subtype, grade, histology and preoperative MRI were associated with the choice of initial surgery.
Multivariate logistic model to investigate factors associated with initial MAST MAST vs BCS OR95%CIPAge &lt;0.01&lt;501 50-590.70.6 - 0.8 60-690.70.6 - 0.8 70+0.60.5 - 0.7 BMI (kg/m2) &lt;0.01&lt;18.51.81.3 - 2.6 18.5-&lt;251 25-&lt;300.80.7 - 0.9 ≥300.70.6 - 0.8 Unknown0.80.6 - 1.0 Comorbidity 0.0501 1+1.11.0 - 1.3 Race 0.8Non Hispanic white1 Non Hispanic black10.8-1.2 Hispanic10.8-1.3 Other1.10.9-1.4 Insurance 0.16Manged care/ Indemnity1 Medicare10.9-1.2 Self-pay/Medicaid1.31-1.6 Other10.6-1.6 Median Household income 0.021 (low)1 20.90.8-1.1 30.90.8-1.1 40.90.8-1.0 5 (high)0.80.6-0.9 Year of diagnosis11-10.35Center &lt;0.01A1 B0.90.7-1.1 C0.70.6-0.9 D1.41.1-1.7 E0.40.3-0.6 F0.80.6-1.1 G1.31-1.6 H0.60.4-0.8 Clinical Stage &lt;0.01T1a1 T1b0.80.6-0.9 T1c10.8-1.2 T1NOS1.10.9-1.4 Tumor Subtype &lt;0.01HER2+HR+1 HER2+HR-1.51.1-1.9 HER2-HR+0.90.7-1.0 HER-HR-0.70.6-0.9 Grade &lt;0.01Low Intermediate1 High1.21.1-1.4 Histology Ductal1 &lt;0.01Lobular1.41.2-1.7 Mixed1.31.1-1.5 Other0.70.5-0.8 Preoperative MRI No1 &lt;0.01Yes1.81.6-2.1
Conclusions: Among a cohort of pts with small node negative BC, 23% elected to have MAST with significant variation associated with choice of treatment, while some of this variation is likely appropriate and clinically indicated, further studies to assess pt understanding of the tradeoffs between BCS and MAST is warranted. These findings need to be considered in light of the increasing number of pts who are choosing MAST/bilateral MAST.
Citation Format: Ines Vaz Luis, Melissa E Hughes, Angel Cronin, Hope S Rugo, Stephen B Edge, Beverly Moy, Richard Theriault, Michael J Hassett, Eric P Winer, Nancy U Lin. Variation in the use of mastectomy (MAST) in women with small node negative breast cancer (BC) treated at US academic institutions [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-13-03.