title: Biological subtyping of early breast cancer: a study comparing RT-qPCR with immunohistochemistry.
abstract: The biological subtype of breast cancer influences the selection of systemic therapy. Distinction between luminal A and B cancers depends on consistent assessment of Ki-67, but substantial intra-observer and inter-observer variability exists when immunohistochemistry (IHC) is used. We compared RT-qPCR with IHC in the assessment of Ki-67 and other standard factors used in breast cancer subtyping. RNA was extracted from archival breast tumour tissue of 769 women randomly assigned to the FinHer trial. Cancer ESR1, PGR, ERBB2 and MKI67 mRNA content was quantitated with an RT-qPCR assay. Local pathologists assessed ER, PgR and Ki-67 expression using IHC. HER2 amplification was identified with chromogenic in situ hybridization (CISH) centrally. The results were correlated with distant disease-free survival (DDFS) and overall survival (OS). qPCR-based and IHC-based assessments of ER and PgR showed good concordance. Both low tumour MKI67 mRNA (RT-qPCR) and Ki-67 protein (IHC) levels were prognostic for favourable DDFS [hazard ratio (HR) 0.42, 95 % CI 0.25-0.71, P = 0.001; and HR 0.56, 0.37-0.84, P = 0.005, respectively] and OS. In multivariable analyses, cancer MKI67 mRNA content had independent influence on DDFS (adjusted HR 0.51, 95 % CI 0.29-0.89, P = 0.019) while Ki-67 protein expression had not any influence (P = 0.266) whereas both assessments influenced independently OS. Luminal B patients treated with docetaxel-FEC had more favourable DDFS and OS than those treated with vinorelbine-FEC when the subtype was defined by RT-qPCR (for DDFS, HR 0.52, 95 % CI 0.29-0.94, P = 0.031), but not when defined using IHC. Breast cancer subtypes approximated with RT-qPCR and IHC show good concordance, but cancer MKI67 mRNA content correlated slightly better with DDFS than Ki-67 expression. The findings based on MKI67 mRNA content suggest that patients with luminal B cancer benefit more from docetaxel-FEC than from vinorelbine-FEC.
authors.affiliation: STRATIFYER Molecular Pathology GmbH, Werthmannstr. 1c, 50935, Cologne, Germany. ralph.wirtz@stratifyer.de.
authors.forename: Ralph M
authors.initials: RM
authors.lastname: Wirtz
authors.affiliation: Laboratory of Molecular Oncology, Translational Cancer Biology Program, University of Helsinki, Helsinki, Finland.
authors.forename: Harri
authors.initials: H
authors.lastname: Sihto
authors.affiliation: Laboratory of Cancer Biology, Institute of Medical Technology, Tampere, Finland.
authors.forename: Jorma
authors.initials: J
authors.lastname: Isola
authors.affiliation: Department of Pathology, HUSLAB, Helsinki University Hospital and Helsinki University, Helsinki, Finland.
authors.forename: Päivi
authors.initials: P
authors.lastname: Heikkilä
authors.affiliation: Department of Oncology, Tampere University Hospital and University of Tampere, Tampere, Finland.
authors.forename: Pirkko-Liisa
authors.initials: PL
authors.lastname: Kellokumpu-Lehtinen
authors.affiliation: Cancer Center, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Päivi
authors.initials: P
authors.lastname: Auvinen
authors.affiliation: Department of Oncology and Radiotherapy, Oulu University Hospital, Oulu, Finland.
authors.forename: Taina
authors.initials: T
authors.lastname: Turpeenniemi-Hujanen
authors.affiliation: Department of Oncology, Turku University Hospital, Turku, Finland.
authors.forename: Sirkku
authors.initials: S
authors.lastname: Jyrkkiö
authors.affiliation: STRATIFYER Molecular Pathology GmbH, Werthmannstr. 1c, 50935, Cologne, Germany.
authors.forename: Sotiris
authors.initials: S
authors.lastname: Lakis
authors.affiliation: BioNTech Diagnostics GmbH, Mainz, Germany.
authors.forename: Kornelia
authors.initials: K
authors.lastname: Schlombs
authors.affiliation: BioNTech Diagnostics GmbH, Mainz, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Laible
authors.affiliation: Acomed Statistik, Leipzig, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
authors.affiliation: Institute of Pathology at the St-Elisabeth-Hospital, Cologne, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Eidt
authors.affiliation: BioNTech Diagnostics GmbH, Mainz, Germany.
authors.forename: Ugur
authors.initials: U
authors.lastname: Sahin
authors.affiliation: Department of Oncology, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Joensuu
mesh_terms: D014408:Biomarkers, Tumor / Q000235:genetics* / Q000378:metabolism*; D001943:Breast Neoplasms / Q000145:classification* / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D018572:Disease-Free Survival; D000077143:Docetaxel; D055088:Early Detection of Cancer; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000235:genetics / Q000378:metabolism; D015588:Observer Variation; D011379:Prognosis; D011897:Random Allocation; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism; D016019:Survival Analysis; D043823:Taxoids / Q000627:therapeutic use; D014747:Vinblastine / Q000031:analogs & derivatives / Q000627:therapeutic use; D000077235:Vinorelbine
chemical_list: D014408:Biomarkers, Tumor; D000077143:Docetaxel; D047628:Estrogen Receptor alpha; D019394:Ki-67 Antigen; D018719:Erb-b2 Receptor Tyrosine Kinases; D011980:Receptors, Progesterone; D043823:Taxoids; D014747:Vinblastine; D000077235:Vinorelbine; C506487:ESR1 protein, human; C508053:ERBB2 protein, human
keywords: Breast cancer; Immunohistochemistry; Ki-67; Molecular subtypes; Prediction; RT-qPCR