Reducing Uncertainty in Estrogen Receptor (ER) Expression Scoring by IHC

Treatment of breast tumors that strongly express the estrogen receptor (ER-positive) can be significantly different from the treatment of tumors that do not express the estrogen receptor (ER-negative) and assessing the status of ER expression accurately is therefore paramount and a basic first step in breast cancer evaluation.

Comparing Immunohistochemistry (IHC)
and Genomic Testing

The standard methodology most commonly used to measure the expression of the estrogen receptor on tumor cells is Immunohistochemistry (IHC). IHC uses a set of chemistries to highlight, or stain, proteins in a cell to be viewed by a light microscope. A pathologist reads the slides and interprets the level of staining into a “positive” or “negative” score.

To arrive at a positive or negative score, a Pathologists measures the intensity of staining and distribution present within the tumor. This type of measurement is called semi-quantitative scoring. If the IHC score reveals a level of ER staining equal to or greater than 1%, the tumor is called ER-positive, and, conversely, if the amount of staining within the tumor is less than 1%, it is called ER-negative.

For most ER-positive tumors, the tumor tissue is also sent for broader genomic tests, that in addition to providing information on chemotherapy response and risk recurrence, also report the level of expression of the ER gene.

Research has shown that there can be a discrepancy between testing ER expression with immunohistochemistry (IHC) and genomic testing (REF). This inconsistency is generally due to the difficulty of scoring the ER expression by IHC when the protein expression levels are close to the 1% cutoff, or when ER receptor staining is weak. Herein lies the problem that BA-ER addresses.

BA-ER is a single gene ER test that can be performed immediately after a borderline or questionable IHC test less time and money than broader genomic tests. By using the BA-ER test in these IHC borderline cases, the confusion, expense, and uncertainty for the Oncologist and Patient are minimized.

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How BA-ER Fits Into the ER Care Pathway