Breast Cancer Coverage from Every Angle

ASCO and ACS Issue Guideline Update on Endocrine Receptor Testing in Breast Cancer

By: Nahae Kim, MPH
Posted: Friday, March 13, 2020

As part of a guideline update, the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) advise samples with 1% to 10% of cells staining positive for estrogen receptor (ER) expression to be reported as ER-low positive, with a recommended comment. Quality control is a priority, and standard operating procedures in laboratories outlining additional confirmatory steps are recommended.

“Like the original guideline, invasive cancers with 1% to 100% ER staining are considered positive and eligible for endocrine therapy,” stated project co-chair Kimberly Allison, MD, FCAP, of Stanford University of Medicine, California, in a CAP press release. “But this update focuses on better assessment of cases with lower levels of ER expression. This will give physicians and patients more information to guide them when making treatment decisions.”

The guideline recommends that ER-low positive pathology reports should be accompanied with reports of percentage of cells staining, intensity, status of controls, and additional comments stating the limited evidence of endocrine therapies for this subset of patients. Current data suggest that invasive cancers with ER-low positivity frequently have gene-expression profiles akin to those of ER-negative cancers. Standard operating procedures are recommended, with a special emphasis on the evaluation of controls. For ER-low positive cases, the status of internal controls should be reported; if the status is not available, another report comment should be provided.

Validated immunohistochemistry remains the standard procedure for predicting therapeutic value from endocrine therapy. Furthermore, estrogen receptors should be tested in cases of newly diagnosed ductal carcinoma in situ, whereas progesterone receptor testing is optional for this subset of patients, as data supporting its benefit are lacking. However, progesterone receptor testing is still recommended for patients with estrogen receptor–positive invasive cancer, mainly as a prognostic tool.

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