Reproducibility of mrna-based testing of esr1, pgr, erbb2, and mki67 expression in invasive breast cancer—a europe-wide external quality assessment

Ramona Erber, Arndt Hartmann, Peter Andreas Fasching, Matthias Ruebner, Robert Stöhr, Matthias Wilhelm Beckmann, Miriam Zentgraf, Verena Popp, Jodi Weidler, Iris Simon, Steffi Becker, Hanna Huebner, Josephine Fischer, Elena Guerini Rocco, Giuseppe Viale, Anne Cayre, Frederique Penault-Llorca, Tamara Caniego Casas, Belén Pérez-Miés, José PalaciosPaul Jank, Carsten Denkert, Lina Khoury, Thomas Mairinger, Fulvia Ferrazzi

Research output: Contribution to journalArticlepeer-review


Estrogen receptor (ER), progesterone receptor (PgR), Ki-67, and HER2 immunohistochemistry (IHC) together with HER2 in situ hybridization (ISH) are utilized to classify invasive breast cancer (IBC) into predictive molecular subtypes. As IHC evaluation may be hampered by analytical errors, gene expression assays could offer a reliable alternative. In this first Europe-wide external quality assessment (EQA) study, we investigated performance of mRNAbased Xpert® Breast Cancer STRAT4 (CE-IVD) in five European laboratories. The cohort comprised ten pre-therapy IBC core biopsies diagnosed in the coordinating center (CC). STRAT4 binary (positive or negative) mRNA results of each marker (ESR1, PGR, ERBB2, MKI67) were compared with the gold standard IHC/ISH performed by the CC. Sensitivity, specificity, and accuracy of ESR1 and ERBB2 mRNA were 100% for all samples. In contrast, PGR expression was falsely negative for one case by two sites and MKI67 falsely negative for two cases (respectively by four and one sites). These cases had STRAT4 expression values close to assay cut-offs and immunohistochemically presented heterogeneous low positive PgR and heterogeneous Ki-67. Our EQA shows that STRAT4 mRNA assay may be a reproducible method to evaluate ER, PgR, HER2, and Ki-67 status. However, cases with expression values close to assay cut-offs should be carefully reviewed.

Original languageEnglish
Article number4718
Issue number18
Publication statusPublished - Sep 2021


  • Breast cancer
  • ERBB2
  • ESR1
  • GeneXpert
  • MKI67
  • MRNA expression testing
  • PGR
  • STRAT4
  • Xpert

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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