A method employing fluorescent detection appears to be more adept than conventional immunohistochemistry in identifying estrogen receptor (ER)-positive breast cancers.

Immunohistochemistry detects the presence of specific proteins in cancer tissue to determine whether a tumor is ER-negative or ER-positive, designations that guide treatment choices. However, researchers have now found that 10% to 20% of cases deemed ER-negative are, in fact, ER-positive. Patients whose tumors are incorrectly classified as ER-negative may be treated with less effective therapies than tamoxifen or other endocrine treatments reserved for ER-positive tumors.

“Our research shows that the conventional methods of measurement of estrogen receptor may result in a 10% to 20% false negative rate,” confirmed David Rimm, MD, professor of pathology at Yale School of Medicine in New Haven, Connecticut, in a statement announcing the findings of the investigative team he led at Yale Cancer Center.

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As Rimm and colleagues reported online for the Journal of Clinical Oncology, they used a novel method to detect ER that proved to be more sensitive and reproducible in uncovering cases of breast cancer initially classified as ER-negative that behave as ER-positive. These patients had prognostic outcomes similar to ER-positive patients.

The assay quantifies ER by analyzing ER immunoreactivity through immunoblotting and immunofluorescence. Now licensed to HistoRx Inc of Branford, Connecticut, the test will soon be available to patients in labs certified under Medicare’s Clinical Laboratory Improvement Amendments (CLIA) program.