Long-term results of breast-conservation therapy for Japanese women classified according to intrinsic subtype

Abstract

e11578 Background: Microarray analysis has identified breast cancer subtypes with distinct gene expression profiles according to the estrogen receptor (ER) and the human epidermal growth factor 2 (HER2) expression. The luminal subtypes (ER-positive) appear to be associated with the better prognosis, whereas the basal and HER2 subgroups tend to have worse recurrence rates. The impact of intrinsic subtype for Japanese women with early-stage invasive breast cancer on prognosis is unknown. The purpose of this study is to address whether breast cancer subtype is associated with recurrence among Japanese women who receive breast-conservation therapy (BCT). Methods: The study cohort included 770 consecutive women with invasive breast cancer who received BCT at University of Tokyo Hospital from 1994 through 2007. Among them, 285 women had complete information on the ER and HER2 status of their primary tumors. The number of patients according to luminal A (ER+HER2- ), luminal B (ER+ HER2+), basal (ER-HER2-) and HER2 (ER-HER2+) subtype was 162, 66, 40 and 17, respectively. All patients received external-beam radiation therapy to the whole breast. The most common doses were 50 Gy in 25 fractions to the whole breast plus a tumor-bed boost to 60 Gy. Results: Median follow-up time was 55 months (range, 6 to 144 months). No significant difference was observed between 5-year disease control and four major subtypes. The 5-year relapse free survival rate of HER2-positive and -negative patients was 77% vs. 95%, which was of statistically significance (p = 0.001). Multivariate analysis showed that T stage, N stage, HER2 status and lymphatic vessel invasion correlated significantly with shorter relapse free survival. Multivariate analysis showed that only N stage was associated with decreased overall survival (p = 0.017). Conclusions: Overall, the 5-year relapse free survival rate after BCT was high, and no significant difference was found in four major subtypes as approximated using ER and HER2 status in Japanese women who receive BCT. Only HER2 status was a statistically significant risk factor after BCT. Although further follow-up is needed, BCT may still be optimal option in Japanese women with early-stage invasive breast cancer to whichever intrinsic subtype their tumors belong. No significant financial relationships to disclose.