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Potential for False-Positive Staining With a Rabbit Monoclonal Antibody to Progesterone Receptor (SP2)
Findings of the UK National External Quality Assessment Scheme for Immunocytochemistry and FISH Highlight the Need for Correct Validation of Antibodies on Introduction to the Laboratory

Merdol Ibrahim PhD, Andrew Dodson MSc, Sarah Barnett MSc, David Fish MSc, Bharat Jasani PhD, Keith Miller MSc
DOI: http://dx.doi.org/10.1309/2YXRLEQVPPNRWHGA 398-409 First published online: 1 March 2008


This study focused on recent assessment results from the United Kingdom National External Quality Assessment Scheme for Immunocytochemistry and Fluorescence In-Situ Hybridisation breast hormone receptor module in which participants were asked to demonstrate progesterone receptors (PRs). The slides consisted of 3 infiltrating ductal breast carcinomas, previously classified as a high PR expresser, a moderate to low PR expresser, and a negative tumor.

During this assessment, 2 commercial rabbit monoclonal antibodies, SP2 (Lab Vision/NeoMarkers, Fremont, CA), and 1E2 (Ventana, Tucson, AZ) were used by 15% of the participants. The SP2 rabbit monoclonal antibody showed false-positive and nonspecific staining on the previously established PR– tumor. This article highlights the necessity for all clinical laboratories to validate immunohistochemical methods and protocols when using newly marketed antibodies such as SP2; use composite tissue blocks with known levels of tumor expression such as a high, mid, and negative expression; and participate in internal and external quality assessment schemes, which can highlight potential technical issues in laboratory methods.

Key Words:
  • Breast hormonal receptors
  • Progesterone receptor
  • Rabbit monoclonal antibody
  • SP2
  • Quality assurance
  • Antibody validation