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

Am J Clin Pathol. 2008 Mar;129(3):398-409. doi: 10.1309/2YXRLEQVPPNRWHGA.


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.

MeSH terms

  • Animals
  • Antibodies, Monoclonal*
  • Breast Neoplasms / metabolism
  • Carcinoma, Ductal, Breast / metabolism
  • Cross Reactions
  • False Positive Reactions
  • Female
  • Humans
  • Immunohistochemistry / standards*
  • Laboratories / standards*
  • Pathology, Clinical / standards*
  • Quality Assurance, Health Care*
  • Rabbits
  • Receptors, Progesterone / immunology
  • Receptors, Progesterone / metabolism*
  • United Kingdom


  • Antibodies, Monoclonal
  • Receptors, Progesterone