- Breast tumors with 1%-10% estrogen receptor (ER)-positive staining should be newly categorized as "ER Low Positive," according to an updated guideline by an international panel of the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP).
- The new category should be accompanied by a comment that "limited data ... suggest possible benefit" of endocrine treatment.
- No similar change was recommended for the progesterone receptor (PR).
- The new guidelines carry 3 other multipart recommendations.
Why this matters
- More than 1 million women per year worldwide are tested for this type of breast cancer.
- The purpose of the new ER Low Positive category and other categories is to promote endocrine therapy, assist in prognostication, and be a diagnostic aid in metastatic breast cancer.
- Recommendations developed by a review of the medical literature by an international multidisciplinary panel.
- Funding: ASCO.
- Clinicians should be able to discuss with patients the limited data behind the ER Low Positive category.
- Patients with ductal carcinoma in situ should be tested for ER, whereas testing for PR should be optional.
- A sample is considered ER− when
- Reporting of initial low to no ER immunoreactivity should include a new laboratory-specific standard operating procedure to confirm/adjudicate results.