IHC is an established assay to determine the ER/PgR status of a tumor by measuring protein amounts of ER and PgR in breast cancer cells. However, up to 10% - 20% of IHC test results throughout the world may be inaccurate (false positive or false negative).

The American Society of Clinical Oncology (ASCO; Alexandria, VA, USA) and the College of American Pathologists (CAP; Washington DC, USA) conducted a systematic review of medical research literature in partnership with Cancer Care Ontario (Toronto, Canada) to develop the recommendations. The guideline was published in the April 19, 2010, issues of ASCO's Journal of Clinical Oncology (JCO) and the CAP's Archives of Pathology & Laboratory Medicine.

The guideline recommends the following: testing ER and PgR status on all newly diagnosed invasive breast cancers (primary site and/or metastatic site), and repeat testing in patients with a known breast cancer diagnosis who then present with a local or distant recurrence; establishing uniform testing measures that focus on proven, reliable, and reproducible assays and procedures; having testing laboratories validate their assays against existing and clinically validated tests; transporting breast tissue specimens from the operating room to the pathology laboratory as soon as they are available for gross assessment; performing ER and PgR testing in a CAP-accredited laboratory or in a laboratory that meets the accreditation requirements spelled out in the guideline; and considering an ER and PgR test performed by an IHC assay as positive if at least one percent of the tumor in the sample tests positive.

About 20 % of all women with invasive breast cancer are HER2-positive, meaning they overexpress HER2, and about 15 % of breast cancers do not express HER2, ER, or PgR receptors (triple-negative). Accurate determination of tumor phenotype is critical to properly select therapy options and individualize treatments.

The panel agreed that it is reasonable for oncologists to discuss the pros and cons of endocrine therapy with patients whose tumors contain low levels of ER by IHC (one percent to ten percent weakly positive cells) and to make an informed decision based on available information.

For the clinical practice guideline and other resources please see related links below. ASCO also has developed a corresponding patient guide available on ASCO's patient website, also given below .

Related Links:
American Society of Clinical Oncology
College of American Pathologists
The Clinical Practice Guidelines
ASCO Patient Guide