Abstract P5-02-12: Concordance between semiquantitative immunohistochemical assay and oncotype DX RT-PCR assay for estrogen and progesterone receptors

Introduction: Estrogen receptor (ER) and progesterone receptor (PR) expression are generally determined by semiquantitative immunohistochemistry (IHC) as recommended in the clinical practice guidelines of the American Society of Clinical Oncologists. This method may be subject to variability because of differences in fixation, ER antibody clones, as well as to immunostain interpretation and use of arbitrary cut-off points. Materials and methods: We identified 72 breast cancer cases at Basurto University Hospital from 1 September 2012 to 31 May 2014 that have been analyzed by Oncotype DX with reporting on ER/PR expression levels by RT-PCR (Genomic Health Inc, Redwood City, CA). According to the company’s report, a tumor is considered as ER positive with expression units of >=6.5 and PR positive with expression units of >=5.5. Oncotype DX is a commercial assay that predicts tumor recurrence in node-negative ER-positive breast cancers. It is a reverse transcription-polymerase chain reaction (RT-PCR) based assay that analyzes the expression of 21 genes (16 cancer-related and 5 control genes) to provide a distant disease recurrence score ranging from 0 to 100. At our institution, hormone receptors by IHC were analyzed on corresponding surgery breast specimens at the time of initial diagnosis. They were evaluated by IHC on formalin-fixed paraffin-embedded tissue, between 8-72 hours. ER was assessed using Roche antibody clone SP1 and PR was assessed using antibody clone 1E2. Percentage of positive nuclei was determined by visual microscopic estimation: Citation Format: Patricia Novas, Elena Galve, Sara Fernández, Maria Ángeles Sala, Alberto Arévalo, Juan Arango, Borja López de San Vicente, Seila Fernández, Ane Zumárraga, Purificación Martínez del Prado. Concordance between semiquantitative immunohistochemical assay and oncotype DX RT-PCR assay for estrogen and progesterone receptors [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-02-12.