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 < 0.01). The proportion of subtypes in SBC and MBC were as follows: luminalA, 65.8% vs. 45.0%; luminalB, HER2+, 9.0% vs. 8.5%; HER2-enriched, 4.1% vs. 12.1%; and TN, 11.2% vs. 31.2%, respectively (P < 0.01). The 10-year overall survival rate in patients with SBC and MBC was 89.0% and 93.6%, respectively. The 10-year disease-free survival rate in patients with SBC and MBC was 79.6% and 80.9%, respectively. Locoregional recurrence was found in 2.5% of patients with SBC and 9.9% of patients with MBC. Distant metastasis occurred in 8.7% of patients with SBC and 4.9% of patients with MBC. Conclusion: The distribution of breast cancer subtypes was different between SBC and MBC. TN-subtype was profoundly more frequent in MBC whereas luminal-subtype was most frequently found among SBC.