ER/PgR Testing in Breast Cancer Clinical Practice Guidelines (ASCO/CAP, 2020)

American Society of Clinical Oncology/College of American Pathologists

This is a quick summary of the guidelines without analysis or commentary. For more information, go directly to the guidelines by clicking the link in the reference.

January 31, 2020

The guideline update on estrogen receptor (ER) and progesterone receptor (PR) testing in breast cancer was released on January 13, 2020 by the American Society of Clinical Oncology and the College of American Pathologists.[1]

ER testing of invasive breast cancers by validated immunohistochemistry remains the standard for predicting which patients may benefit from endocrine therapy; no other assays are recommended for this purpose.

Breast cancer samples with 1% to 100% of tumor nuclei positive should be interpreted as ER positive. However, data on the benefit of endocrine therapy for cancers with 1-10% of cells staining ER positive are limited. Samples with these results should be reported using a new reporting category, ER Low Positive, with a recommended comment.

A sample is considered ER negative if < 1% or 0% of tumor cell nuclei are immunoreactive.

For cases in which the initial result is low to no ER staining, additional strategies recommended to promote optimal performance, interpretation, and reporting include establishing a laboratory-specific standard operating procedure describing additional steps used by the laboratory to confirm/adjudicate results. The status of controls should be reported for cases with 0% to 10% staining.

Similar principles apply to PR testing, which is used primarily for prognostic purposes in the setting of an ER-positive cancer. Testing of ductal carcinoma in situ (DCIS) for ER is recommended to determine potential benefit of endocrine therapies to reduce risk of future breast cancer, while testing of DCIS for PR is considered optional.

For more information, see Breast Cancer. For more Clinical Practice Guidelines, please go to Guidelines.

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