Concordance between Semi-Quantitative Immunohistochemical Assay and oncotypeDX RT-PCR Assay for Estrogen and Progesterone Receptors
R Bhargava, S Beriwal, DJ Dabbs. Magee-Womens Hospital of UPMC, Pittsburgh, PA
Background: The 21 gene reverse transcriptase polymerase chain reaction (RT-PCR) assay, commercially available as oncotypeDXTM (Genomic Health Inc., Redwood City, CA) is increasingly used in clinical decision making for estrogen receptor (ER)+, lymph node negative breast cancer patients. The company has recently initiated separate reporting of ER and progesterone receptor (PR) expression units (compared to reference genes).
Design: As part of our quality assurance measures, we compared the ER and PR RT-PCR results with the semi-quantitative immunohistochemistry (IHC) on 80 patients. The ER and PR RT-PCR results (performed on resection specimens) were obtained from Genomic Health reports. The RT-PCR test classifies a tumor as ER or PR positive if the expression units are 6.5 or 5.5 respectively. ER (clone SP1) and PR (clone 1E2) IHC was performed on optimally fixed core breast biopsy samples and semi-quantitation was performed using a modified H-score method which takes into account both intensity and proportion of cellular staining and the score ranges from 0-300. Any nuclear staining by IHC was considered positive. The results of RT-PCR versus IHC were compared qualitatively (positive/negative) and quantitatively using Spearman rank correlation.
Results: Since oncotypeDXTM is currently performed only on ER+ tumors, all 80 tumors in this study were positive for ER by IHC. All these tumors were also identified as ER+ by RT-PCR. Of the 80 cases, 70 were positive and 5 were negative for PR by both tests. The remainder 5 cases were positive by IHC, but negative by RT-PCR. These cases showed weak PR immunoreactivity (mean H-score of 5.8 and range of 2-15). A linear correlation was obtained between RT-PCR and IHC results for both ER (RT-PCR units range: 7.1-12; H-score range: 14-300; correlation coefficient of 0.509) and PR (RT-PCR units range: 3.2-10; H-score range: 0-300; correlation coefficient of 0.664).
Conclusions: The study demonstrated a high degree of concordance between RT-PCR and IHC for both ER (100%) and PR (94%). The study also demonstrates concordance of hormone receptor (HR) results between core biopsy and resection specimens. There was good linear correlation between IHC semiquantitative results and receptor expression levels determined by RT-PCR. The added advantage of IHC is preservation of morphology and accurate assessment of invasive tumors that are admixed with abundant in-situ carcinoma or normal breast tissue. Moreover, IHC can be performed on the same day of biopsy interpretation.
Wednesday, March 11, 2009 9:30 AM
Poster Session V # 5, Wednesday Morning