1. ¹Center for Molecular Oncologic Pathology, Dana Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
2. ²Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
3. ³Department of Medical Oncology, Harvard Medical School, Dana Farber Cancer Institute, Boston, MA, USA

Correspondence: Dr M Loda, MD, Dana Farber Cancer Institute, Dana Building, 15th Floor, D1536 Boston, MA 02115, USA. E-mail: Massimo_loda@dfci.harvard.edu

Received 11 February 2009; Revised 10 April 2009; Accepted 10 April 2009; Published online 1 June 2009.

Abstract

Breast carcinoma cells with the CD44⁺/CD24^low phenotype have been reported to exhibit 'cancer stem cell' (CSC) characteristics on the basis of their enhanced tumorigenicity and self-renewal potential in immunodeficient mice. We used immunohistochemistry to study the expression of these proteins in whole tissue sections of human breast carcinoma. We found that the fraction of CD44v6⁺ cells is higher in estrogen receptor-positive carcinomas after neoadjuvant chemotherapy. We also performed double immunohistochemistry for CD44v6 and for the proliferation marker Ki67. We found that the relative number of quiescent carcinoma cells is higher in the CD44v6⁺ population than in the CD44v6- population in specific carcinoma subtypes. We then used quantum dots and spectral imaging to increase the number of antigens that could be visualized in a single tissue section. We found that anti-CD44v6 and CD24 antibodies that were directly conjugated to quantum dots retained their ability to recognize antigen in formalin-fixed, paraffin-embedded tissue sections. We then performed triple staining for CD44v6, CD24 and Ki67 to assess the proliferation of each sub-population of breast carcinoma cells. Our results identify differences between CD44v6-positive and CD44v6-negative breast carcinoma cells in vivo and provide a proof of principle that quantum dot-conjugated antibodies can be used to study specific sub-populations of cancer cells defined by multiple markers in a single tissue section.