An update to the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) clinical practice guideline on estrogen receptor (ER) and progesterone receptor (PgR) testing in breast cancer, published in the Journal of Clinical Oncology, provided details on optimizing the assay algorithm, as well as optimal testing conditions, tissue handling, assay validation, and laboratory accreditation procedures.

First released in 2010, the ASCO/CAP guideline on ER and PgR testing in breast cancer was developed by an expert panel based on a systematic review of the literature and “aimed at improving the analytic performance and diagnostic accuracy of ER and PgR testing and their clinical utility as biomarkers for the management of women with primary breast cancer.”

Some of the recommendations included in the 2020 clinical practice guideline update on ER and PgR testing in breast cancer were as follows:

  • Immunohistochemistry (IHC) should remain as the only primary screening assay used to predict benefit from endocrine therapy in breast cancer
  • All tumor specimens with at least 1% tumor cell nuclei immunoreactive for ER or PgR are considered hormone receptor-positive,
    • With the caveat that tumors with 1% to 10% of tumor cell nuclei immunoreactive for ER should be reported as “ER-low positive” along with a comment including specific recommendations
    • Conversely, tumor specimens with less than 1% tumor cell nuclei immunoreactive for ER or PgR are considered hormone receptor-negative
  • Large, multiple-core biopsies of tumor are preferred and the time between sample acquisition and fixation should be as short as possible
    • Fixation is done in 10% neutral buffered formalin for between 6 and 72 hours, and the details of fixation should be recorded
  • Provision of details related to internal validation of the ER or PgR test assay was deferred to the forthcoming CAP guideline update on this topic
  • Internal quality assurance should involve ongoing training and competency assessment of laboratory personnel
  • The testing laboratory must participate in external proficiency testing or alternative performance assessment as specified by accrediting organization
  • Laboratory accreditation should involve on-site inspection every other year as well as self-inspection annually
  • Validated ER testing by IHC was recommended in the setting of newly diagnosed ductal carcinoma in situ (DCIS)

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Additional details, such as the topics that should be covered in standard operating procedures (SOPs) for ER and PgR testing in breast cancer, as well as strategies to facilitate interpretation and reporting of specific scenarios (eg, ER-low positive) or the absence of internal controls, and examples of specific cases, were provided in the published version of the ASCO/CAP guideline update on ER and PgR testing in breast cancer.

Reference

Allison KH, Hammond MEH, Dowsett M, et al. Estrogen and progesterone receptor testing in breast cancer: ASCO/CAP guideline update. J Clin Oncol. doi: 10.1200/JCO.19.02309