Publication Year: 2000 Visited: 167

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Discrepancies in Laboratory Assessment of Eligibility for Herceptin Therapy: The Message Matters. Raymond Tubbs, Pat Roche, Mark Stoler, James Pettay, Robert Jenkins, Jonathan Myles, Thomas Grogan, Cleveland Clin, Cleveland, OH; Mayo Clin, Rochester, MN; Univ of Virginia Sch of Medicine, Charlottesville, VA; Univ of Arizona Health Science Ctr, Tucson, AZ.

Objectives: Previous studies have reported apparent false-positive results using HercepTest to profile Her-2/neu amplification/overproduction in breast carcinoma. False-positive status has been based on comparisons with gene copy enumeration by FISH and with comparisons to immunohistochemistry (IMH) results using a monoclonal antibody. But simple overexpression of oncoprotein by tumor cells having normal gene copy has not been evaluated by measuring mRNA expression--these apparent discrepancies may simply represent true positive overexpression in the absence of gene amplification. Methods: 100 infiltrating ductal carcinomas of breast were evaluated by FISH using digoxigenin labeled probes, mRNA detection by autoradiographic RNA:RNA in situ hybridization, and IMH using monoclonal (CB11) (Ventana) and polyclonal (HercepTest) (Dako) antibodies following antigen retrieval (AR). Results: mRNA expression was highly concordant with FISH and with CB11 immunohistology. 15 of 100 cases were apparent HercepTest false positive by comparative FISH and CB11 immunohistology; neither gene copy (by FISH) nor mRNA levels (by RNA:RNA autoradiographic in situ hybridization) were amplified in the 15 discordant samples. 10 of the 15 cases that were discrepant with mRNA results were 2+ by HercepTest. Conclusion: Based upon correlative mRNA expression we conclude that discordant HercepTest results, as compared to FISH and CB11 IMH, and as compared to mRNA detection, are most commonly actual false-positive results.