Impact of estrogen receptor α on the tamoxifen response and prognosis in luminal-A-like and luminal-B-like breast cancer

The luminal-A-like and luminal-B-like breast cancer groups have distinct biological features that lead to differences in the treatment response and clinical outcome. The aim of this study was to examine the value of the distribution pattern of ERα expression, ESR1 SNPs as well as ESR1 mRNA expression in predicting tamoxifen response and survival in patients with luminal-A-like and luminal-B-like breast cancer. A total of 135 patients with both subtypes were stratified into two groups depending on the tamoxifen response: tamoxifen-resistant patients (TR) and tamoxifen-sensitive patients (TS). ESR1 mRNA expression was measured by real-time quantitative reverse transcription-PCR. Three polymorphisms of ESR1 (rs2077647, rs2228480 and rs1801132) were genotyped using a TaqMan assay. The distribution pattern of ERα expression was analyzed immunohistochemically using the visual assessment of staining. The primary endpoint was progression-free survival (PFS). There was a significant decrease in ESR1 mRNA expression level in the TR group when compared to the TS group among patients with luminal-B-like subtype (P = 0.038). ESR1 2014AA mutant genotype of rs2228480 was more prevalent in the TR patients with luminal-B-like subtype than the TS group (P = 0.045). In the luminal-A-like group, tamoxifen-resistant tumors were more frequently heterogeneous for ERα expression than tamoxifen-sensitive tumors (P = 0.016). Multivariate analysis showed a strong association of lymph node status and the distribution pattern of ERα expression with tamoxifen responsiveness in this cohort of patients. In addition, a luminal-A-like patients with the heterogeneous ERα expression had a significantly shorter PFS time than those with the homogeneous ERα (P = 0.013). These results indicate that the heterogeneous expression of ERα is an accurate predictor of tamoxifen response and survival in luminal-A-like breast cancer patients. ESR1 rs2228480 may act as a marker with a high prognostic potential in luminal-B-like tumors.