<div><p>Introduction</p><p>Amplification of the <i>ESR1</i> gene, coding for estrogen receptor alpha, was shown to predict responsiveness to tamoxifen, however its prognostic impact in breast cancer patients has not been thoroughly investigated. Other factors that could contribute to responsiveness to tamoxifen treatment are polymorphisms in <i>ESR1</i> gene and genes involved in tamoxifen metabolism.</p> <p>The aim of this study was to assess the prognostic role of <i>ESR1</i> gene dosage in a consecutive group of breast cancer patients and to correlate this feature with clinico-pathological factors. Additionally, <i>ESR1</i> PvuII, <i>CYP2C19*2</i> and <i>UGT2B15*2</i> polymorphisms were analyzed in the tamoxifen-treated subgroup of patients.</p> <p>Materials and Methods</p><p>Primary tumor samples from 281 stage I-III consecutive breast cancer patients were analyzed for <i>ESR1</i> gene dosage using real-time PCR with locked nucleic acids hydrolysis probes. In the tamoxifen-treated subgroup of patients, <i>ESR1</i> PvuII, <i>CYP2C19*2</i> and <i>UGT2B15*2</i> polymorphism in leukocytes genomic DNA were analyzed. Results were correlated with clinico-pathological factors and with disease-free survival (DFS) and overall survival (OS).</p> <p>Results</p><p><i>ESR1</i> amplification (with a cut-off level of 2.0) was found in 12% of the entire group of breast cancer patients, and in 18% of the ER-negative subgroup. This feature was associated with decreased DFS both in the entire group (<i>P</i>=0.007) and in the ER-negative subgroup (<i>P</i>=0.03), but not in the tamoxifen-treated patients.</p> <p>Patients with <i>ESR1</i> PvuII wt/wt genotype and at least one <i>UGT2B15</i> wt allele had a worse DFS (<i>P</i>=0.03) and showed a trend towards decreased Os (<i>P</i>=0.08) in comparison to patients with <i>ESR1</i> PvuII wt/vt or vt/vt genotype and <i>UGT2B15</i> *2/*2 genotype.</p> <p>Conclusions</p><p><i>ESR1</i> amplification can occur in ER-negative tumors and may carry poor prognosis. In the tamoxifen-treated subgroup, poor prognosis was related to the combined presence of <i>ESR1</i> PvuII wt/wt and <i>UGT2B15</i>wt/wt or wt/*2 genotype.</p> </div
