Distribution of tumor subtypes in bilateral breast cancer: Comparison between synchronous and metachronous cancer

AIM This study was performed to evaluate patterns of breast cancer subtypes in Korean patients with synchronous (SBC) or metachronous bilateral breast cancer (MBC). METHODS We retrospectively reviewed records of 302 patients with SBC (n = 161) or MBC (n = 141) who received curative surgery at our hospital between 1995 and 2013. Expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) was determined by immunohistochemistry (IHC) staining. We categorized breast cancers into the following subtypes: ER+ or PR+, HER2- (i.e., luminalA); ER+ or PR+, HER2+ (i.e., luminalB HER2+); ER-, PR- and HER2+ (i.e., HER2-enriched); ER-, PR- and HER2- (i.e., triple negative, TN). RESULTS More patients with MBC were ≤40 years at the time of breast cancer diagnosis than patients with SBC (34.6% vs. 19.3%, P