title: High protein expression of EZH2 is related to unfavorable outcome to tamoxifen in metastatic breast cancer.
abstract: BACKGROUND
  Metastatic breast cancer (MBC) is a highly heterogeneous disease with great differences in outcome to both chemo- and endocrine therapy. Better insight into the mechanisms underlying resistance is essential to better predict outcome to therapy and to obtain a more tailored treatment approach. We have previously described that increased mRNA expression levels of Enhancer of Zeste homolog (EZH2) are associated with worse outcome to tamoxifen therapy in MBC. Here, we explored whether this is also the case for EZH2 protein expression.
  
  
  METHODS
  A tissue microarray (TMA) was created using formalin-fixed, paraffin-embedded estrogen receptor (ER)-positive primary breast tumor tissues of 250 MBC patients treated with first-line tamoxifen. Quantity and intensity of EZH2 expression were determined by immunohistochemistry (IHC) and both were used to generate and group scores according to a previously described method for scoring EZH2.
  
  
  RESULTS
  In total, 116 tumors (46%) were considered to be EZH2 positive. The presence of EZH2 protein expression was significantly associated with progression-free survival (PFS) in both univariate [hazard ratio (HR) 1.51, 95% confidence interval (CI) 1.17-1.97, P = 0.002] and multivariate analysis including traditional factors associated with tamoxifen outcome (HR 1.41, 95% CI 1.06-1.88, P = 0.017). Considering quantity irrespective of intensity, tumors with >50% EZH2-positive cells had the worst PFS (HR 2.15, 95% CI 1.42-3.27, P < 0.001), whereas intensity alone did not show a significant association with PFS. Application of other methods of scoring EZH2 positivity resulted in a similar significant association between the amount of EZH2 positive cells and PFS.
  
  
  CONCLUSIONS
  In addition to EZH2 mRNA levels, these results suggest that protein expression of EZH2 can be used as a marker to predict outcome to tamoxifen therapy. This provides new rationale to explore EZH2 inhibition in the clinical setting and increases the possibilities for a more personalized treatment approach in MBC patients.
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: E A
authors.initials: EA
authors.lastname: Reijm
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: A M
authors.initials: AM
authors.lastname: Timmermans
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: M P
authors.initials: MP
authors.lastname: Look
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: M E
authors.initials: ME
authors.lastname: Meijer-van Gelder
authors.affiliation: Department of PATHAN BV, Laboratory Pathology, Sint Franciscus Hospital, Rotterdam, The Netherlands.
authors.forename: C K
authors.initials: CK
authors.lastname: Stobbe
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands; Department of Pathology, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam.
authors.forename: C H M
authors.initials: CHM
authors.lastname: van Deurzen
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: J W M
authors.initials: JWM
authors.lastname: Martens
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Sleijfer
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: J A
authors.initials: JA
authors.lastname: Foekens
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands. Electronic address: p.berns@erasmusmc.nl.
authors.forename: P M J J
authors.initials: PMJJ
authors.lastname: Berns
authors.affiliation: Department of Medical Oncology, Cancer Genomics Netherlands.
authors.forename: M P H M
authors.initials: MPHM
authors.lastname: Jansen
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D018572:Disease-Free Survival; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D000071221:Enhancer of Zeste Homolog 2 Protein; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008875:Middle Aged; D009362:Neoplasm Metastasis; D063151:Polycomb Repressive Complex 2 / Q000096:biosynthesis* / Q000235:genetics; D057285:Precision Medicine; D011379:Prognosis; D012333:RNA, Messenger / Q000096:biosynthesis; D013629:Tamoxifen / Q000008:administration & dosage* / Q000009:adverse effects; D046888:Tissue Array Analysis; D016896:Treatment Outcome
chemical_list: D012333:RNA, Messenger; D013629:Tamoxifen; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2
keywords: EZH2; endocrine therapy resistance; immunohistochemistry; metastatic breast cancer; personalized medicine; tissue microarray