Originally published as JCO Early Release 10.1200/JCO.2005.05.4155 on November 20 2006

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Immunohistochemical Detection Using the New Rabbit Monoclonal Antibody SP1 of Estrogen Receptor in Breast Cancer Is Superior to Mouse Monoclonal Antibody 1D5 in Predicting Survival

Maggie C.U. Cheang, Diana O. Treaba, Caroline H. Speers, Ivo A. Olivotto, Chris D. Bajdik, Stephen K. Chia, Lynn C. Goldstein, Karen A. Gelmon, David Huntsman, C. Blake Gilks, Torsten O. Nielsen, Allen M. Gown

From the Genetic Pathology Evaluation Centre at Vancouver General Hospital, Prostate Centre, and University of British Columbia; Breast Cancer Outcomes Unit and Population and Preventive Oncology Programs at BC Cancer Agency, Vancouver, British Columbia, Canada; and PhenoPath Laboratories, Seattle, WA

Address reprint requests to Torsten O. Nielsen, Anatomical Pathology, JP 1401, Vancouver Hospital & Health Sciences Centre, 855 West 12th Ave, Vancouver, BC, V5Z 1M9, Canada; e-mail: torsten{at}interchange.ubc.ca

PURPOSE: Estrogen receptor (ER) expression predicts improved breast cancer–specific survival and reduced risk of recurrence and is targeted in breast cancer therapy. A high-quality antibody to identify ER-positive patients plays an important role in clinical decision making for women with breast cancer. This study evaluates immunohistochemistry using two anti-ER antibodies, a new rabbit monoclonal antibody (SP1) and the mouse monoclonal antibody (1D5), in relation to biochemical ER assay results and clinical data on survival and adjuvant systemic therapy.

PATIENTS AND METHODS: A population-based tissue microarray series of 4,150 invasive breast cancers was constructed. All patients had staging, pathology, treatment, and follow-up information. The median follow-up was 12.4 years and the median age at diagnosis 60 years. Survival analysis and log-rank tests were used to evaluate the prognostic value of ER status and correlations with clinical data.

RESULTS: Among the 4,105 samples interpretable for both antibodies, SP1 detected ER positivity in 69.5% and 1D5 in 63.1% of cases. Both monoclonal antibodies are demonstrated to be good prognostic indictors for breast cancer–specific and relapse-free survival. In multivariate analysis, including age, tumor size, grade, and lymphovascular and nodal status, SP1 was a better independent prognostic factor than 1D5. Among patients with discrepant ER results, the 8% of patients who were SP1 positive/1D5 negative showed good outcomes, and the 2% SP1-negative/1D5 positive had poor outcomes. Maintaining the same 92% specificity and 98% positive predictive value, SP1 is 8% more sensitive than 1D5 using biochemical assay as gold standard.

CONCLUSION: SP1 represents an improved standard for ER immunohistochemistry assessment in breast cancer.

published online ahead of print at www.jco.org on November 20, 2006.

Supported by a Translation Acceleration grant from the Canadian Breast Cancer Research Alliance, an unrestricted educational grant from sanofi aventis, and the National Institute of Health Strategic Partnering to Evaluate Cancer Signatures program. C.D.B., D.H., and T.O.N. are recipients of Scholar Awards from the Michael Smith Foundation for Health Research.

Presented in part at the 28th San Antonio Breast Cancer Symposium, December 8-11, 2005, San Antonio, TX.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

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