Improved estrogen receptor (ER) test is superior in predicting survival in breast cancer patients

December 20, 2006, Seattle, WA. One of today’s most widely used breast cancer tests may underestimate the number of positive breast cancer patients that may benefit from targeted hormone therapy. A landmark study published in the December 20, 2006 issue of the Journal of Clinical Oncology reports that the use of a new anti-estrogen receptor (ER) antibody reagent for the identification of ER in breast cancer specimens is significantly more sensitive and specific than the current reagents used widely in the United States and around the world. The study was conducted by PhenoPath Laboratories in Seattle, Washington, USA in conjunction with the Genetic Pathology Evaluation Centre at Vancouver General Hospital, Vancouver, British Columbia, Canada and the Breast Cancer Outcomes Unit and Population and Preventive Oncology Programs at BC Cancer Agency, under a grant from the Canadian Breast Cancer Research Alliance.

According to Dr. Allen Gown of PhenoPath Laboratories in Seattle, Washington, “The findings of this study may result in a reassessment of current ER testing methodologies in laboratories throughout the United States and Canada.”

In order to determine the most appropriate therapy for breast cancer patients, all new cases are tested for ER by a method know as immunohistochemistry, which is performed on sections of the tumor cut onto glass slides after the tumor has been fixed and processed in the pathology laboratory. Several different anti-ER antibodies are currently in wide use in the United States, one called 6F11 and the other ID5; both have been previously shown to have similar sensitivities.

This new study evaluates a new anti-ER antibody called SP1 and compares its performance with that of the older 1D5 antibody in a large group of 4,150 patients followed for a median of 12.4 years. The new SP1 antibody was demonstrated to be more sensitive than the older 1D5 antibody, and the SP1 results better predicted response to treatment that targeted the ER receptor (tamoxifen) than 1D5 results. Approximately 8% of the patients were characterized as ER-negative with the older 1D5 reagent (false-negative results) but were positive with the new SP1 antibody, and this group of patients clearly demonstrated improved survival, similar to patients with ER-positive cancers. Extrapolating from this study, as many as 8% of newly diagnosed breast cancer patients may be misclassified as ER-negative using the older testing methodologies and, therefore, inappropriately denied ER-targeted therapy such as tamoxifen.

In an editorial response to the study in the same issue of the Journal of Clinical Oncology, Dr. Mitch Dowsett of the Royal Marsden Hospital in London, England, states “My own laboratory will not switch immediately, but the data are sufficient for us to seriously consider performing our own evaluation of it against the 6F11 antibody.”

Contact Information:

Allen M. Gown, M.D. lab@phenopath.com PhenoPath Laboratories, 551 North 34th Street, Suite 100, Seattle, WA 98103-8675 USA

Telephone: 206-374-9000, 888-927-4366, FAX 206-374-9009 www.phenopath.com

Links:

Journal of Clinical Oncology Abstract

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