Biological subtyping of early breast cancer: a study comparing RT-qPCR with immunohistochemistry

Breast Cancer Res Treat. 2016 Jun;157(3):437-46. doi: 10.1007/s10549-016-3835-7. Epub 2016 May 24.

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.

Keywords: Breast cancer; Immunohistochemistry; Ki-67; Molecular subtypes; Prediction; RT-qPCR.

Publication types

  • Comparative Study

MeSH terms

  • Biomarkers, Tumor / genetics*
  • Biomarkers, Tumor / metabolism*
  • Breast Neoplasms / classification*
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Disease-Free Survival
  • Docetaxel
  • Early Detection of Cancer
  • Estrogen Receptor alpha / genetics
  • Estrogen Receptor alpha / metabolism
  • Female
  • Humans
  • Immunohistochemistry
  • Ki-67 Antigen / genetics
  • Ki-67 Antigen / metabolism
  • Observer Variation
  • Prognosis
  • Random Allocation
  • Real-Time Polymerase Chain Reaction / methods*
  • Receptor, ErbB-2 / genetics
  • Receptor, ErbB-2 / metabolism
  • Receptors, Progesterone / genetics
  • Receptors, Progesterone / metabolism
  • Survival Analysis
  • Taxoids / therapeutic use
  • Vinblastine / analogs & derivatives
  • Vinblastine / therapeutic use
  • Vinorelbine

Substances

  • Biomarkers, Tumor
  • Estrogen Receptor alpha
  • Ki-67 Antigen
  • Receptors, Progesterone
  • Taxoids
  • estrogen receptor alpha, human
  • Docetaxel
  • Vinblastine
  • ERBB2 protein, human
  • Receptor, ErbB-2
  • Vinorelbine