Abstract P2-13-09: Implication of breast-conserving therapy in the subtype era of breast cancer

Abstract Background Molecular subtypes of breast cancer are one of the key factors to predict clinical outcomes in women with breast cancer. Some specific subtypes like triple-negative breast cancer (TNBC) show more aggressive behaviors and worse clinical outcomes than luminal A subtype, thus there are conflicting data regarding optimum local surgical strategy for TNBC. We evaluate the clinical outcomes of women who underwent breast-conserving therapy (BCT) compared to those underwent mastectomy regarding to breast cancer subtypes using a large single center cohort. Methods A total of 5353 women who underwent BCT or mastectomy due to primary breast cancer from 1990 to 2010 were retrospectively reviewed. Cases with initial distant metastases or those with neoadjuvant chemotherapy were excluded. Clinicopathological characteristics, overall survival (OS), and recurrence-free survival (RFS) were analyzed using the Chi-square test, Kaplan-Meier survival analysis, and log-rank test. Cox proportional hazard models were used for multivariate analyses. In order to explore the role of BCT in TNBC, we performed sub-group analysis using patients with TNBC in the cohort. Results BCT was performed in 1866 cases and mastectomy in 3487 cases. The mastectomy group had higher T stage (T2-3: 53.5% vs. 26.5%, p<0.001), higher N stage (N2-3 17.1% vs. 5.1%, p<0.001), and more HER2 over-expression (11.6% vs. 8.3% p<0.001) than the BCT group had. The BCT group consisted of more Luminal A and TNBC subtypes than the mastectomy group. (Luminal A 56.2% vs 41.6%, TNBC 19.9% vs 12.7%, all p<0.001) The 5-year RFS rates of the BCT group in luminal A, B, and TNBC were better than those in the mastectomy group (Luminal A 93.7% vs 89.4%, p<0.001, Luminal B 94.9% vs. 86.3%, p=0.01, and TNBC 92.9% vs 79.8%, p<0.001). However, the 5-year RFS of HER2-enriched subtype was not significantly different according to the operation type (p=0.85). The BCT group in luminal A and TNBC showed better OS than the mastectomy group (Luminal A, p=0.002, TNBC, p<0.001), however, the difference of OS between the BCT and mastectomy groups in luminal B and HER2-enriched subtypes was not significant (p>0.05). In multivariate analyses, T and N stage, breast cancer subtypes, histologic grade, and the status of adjuvant chemotherapy were independent prognostic factors for RFS and OS (all p<0.05). However, The statistical significance of RFS and OS of local therapy, BCT vs. Mastectomy, according to breast cancer subtypes in the univariate analyses disappeared in multivariate analyses (HR for RFS=0.90, 95%CI=0.70-1.16, HR for OS=0.83, 95%CI=0.614-1.122). In the sub-group analysis, BCT showed comparable outcomes compared to mastectomy in patients with TNBC in multivariate analyses. (HR for RFS=0.89, 95%CI=0.38-2.06, HR for OS=1.007, 95%CI=0.987-1.028) Conclusions Clinical outcomes were not affected by surgical approaches regarding to breast cancer subtypes. BCT is an acceptable surgical approach regardless of breast cancer subtype, and even in selective patients with TNBC. Citation Format: Sanghwa Kim, Hyung Seok Park, Jee Ye Kim, Jegyu Ryu, Seho Park, Seung Il Kim. Implication of breast-conserving therapy in the subtype era of breast cancer [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 P2-13-09.