Estrogen-Receptor, Progesterone-Receptor and <i>HER2</i> Status Determination in Invasive Breast Cancer. Concordance between Immuno-Histochemistry and MapQuant™ Microarray Based Assay

<div><p>Background</p><p>Hormone receptor status and <i>HER2</i> status are of critical interest in determining the prognosis of breast cancer patients. Their status is routinely assessed by immunohistochemistry (IHC). However, it is subject to intra-laboratory and inter-laboratory variability. The aim of our study was to compare the estrogen receptor, progesterone receptor and <i>HER2</i> status as determined by the MapQuant™ test to the routine immuno-histochemical tests in early stage invasive breast cancer in a large comprehensive cancer center.</p><p>Patients and Methods</p><p>We retrospectively studied 163 invasive early-stage breast carcinoma with standard IHC status. The genomic status was determined using the MapQuant™ test providing the genomic grade index.</p><p>Results</p><p>We found only 4 tumours out of 161 (2.5%) with discrepant IHC and genomic results concerning ER status. The concordance rate between the two methods was 97.5% and the Cohen’s Kappa coefficient was 0.89.</p><p>Comparison between the MapQuant™ PR status and the PR IHC status gave more discrepancies. The concordance rate between the two methods was 91.4% and the Cohen’s Kappa coefficient was 0.74.</p><p>The <i>HER2</i> MapQuant™ test was classified as « undetermined » in 2 out of 163 cases (1.2%). One <i>HER2</i> IHC-negative tumour was found positive with a high <i>HER2</i> MapQuant™ genomic score. The concordance rate between the two methods was 99.3% and the Cohen’s Kappa coefficient was 0.86.</p><p>Conclusion</p><p>Our results show that the MapQuant™ assay, based on mRNA expression assay, provides an objective and quantitative assessment of Estrogen receptor, Progesterone receptor and <i>HER2</i> status in invasive breast cancer.</p></div