Immunohistochemical assay versus Oncotype DX qRT-PCR assay for estrogen and progesterone receptors
Estrogen receptor status is a strong predictor of response to hormonal therapy in breast cancer patients. Its presence and level of expression have been shown to correlate with time to recurrence in patients undergoing therapy with tamoxifen or aromatase inhibitors. Risk reduction is known to  occur in estrogen receptor-negative, progesterone receptor-positive patients treated with hormonal therapy. Since the 1990s, immunohistochemistry has been the primary method for assessing hormone receptor status. As a component of its Oncotype DX assay, Genomic Health recently began reporting quantitative estrogen and progesterone
receptor results determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR).
As part of an ongoing quality assurance program at Magee-Womens Hospital in Pittsburgh, the authors
reviewed 464 breast cancer cases evaluated for estrogen and progesterone receptor by both immunohistochemistry and the Oncotype DX assay. They found good correlation for estrogen receptor
status between both assays (98.9 percent concordance), with immunohistochemistry being slightly more sensitive. Concordance for progesterone receptor was 94.2 percent between immunohistochemistry
and qRT-PCR, with immunohistochemistry again more sensitive. The results also showed linear correlation between immunohistochemistry H-scores and qRT-PCR expression values for estrogen receptor (correlation coefficient, 0.579) and progesterone receptor (correlation coefficient, 0.685). Due to hormone receptor immunohistochemistry having higher sensitivity and additional advantages—that is, preservation of morphology, less expensive, faster, and more convenient—the authors concluded that immunohistochemistry is preferable to qRT-PCR for determining estrogen and progesterone receptor expression.

Kraus JA, Dabbs DJ, Beriwal S, et al. Semi-quantitative immunohistochemical assay versus Oncotype DX qRT-PCR assay for estrogen and progesterone receptors: an independent quality assurance study. Mod Pathol. 2012;25:869–876.