title: Functional ex vivo assay to select homologous recombination-deficient breast tumors for PARP inhibitor treatment.
abstract: OBJECTIVE
  Poly(ADP-ribose) polymerase (PARP) inhibitors are promising targeted treatment options for hereditary breast tumors with a homologous recombination (HR) deficiency caused by BRCA1 or BRCA2 mutations. However, the functional consequence of BRCA gene mutations is not always known and tumors can be HR deficient for other reasons than BRCA gene mutations. Therefore, we aimed to develop a functional test to determine HR activity in tumor samples to facilitate selection of patients eligible for PARP inhibitor treatment.
  
  
  METHODS
  We obtained 54 fresh primary breast tumor samples from patients undergoing surgery. We determined their HR capacity by studying the formation of ionizing radiation induced foci (IRIF) of the HR protein RAD51 after ex vivo irradiation of these organotypic breast tumor samples. Tumors showing impaired RAD51 IRIF formation were subjected to genetic and epigenetic analysis.
  
  
  RESULTS
  Five of 45 primary breast tumors with sufficient numbers of proliferating tumor cells were RAD51 IRIF formation deficient (11%, 95% CI, 5%-24%). This HR defect was significantly associated with triple-negative breast cancer (OR, 57; 95% CI, 3.9-825; P = 0.003). Two of five HR-deficient tumors were not caused by mutations in the BRCA genes, but by BRCA1 promoter hypermethylation.
  
  
  CONCLUSIONS
  The functional RAD51 IRIF assay faithfully identifies HR-deficient tumors and has clear advantages over gene sequencing. It is a relatively easy assay that can be performed on biopsy material, making it a powerful tool to select patients with an HR-deficient cancer for PARP inhibitor treatment in the clinic.
authors: Department of Genetics, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: Kishan A T
authors: KA
authors: Naipal
authors: Department of Genetics, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: Nicole S
authors: NS
authors: Verkaik
authors: Department of Clinical Genetics, VU University Medical Center, Amsterdam, the Netherlands.
authors: Najim
authors: N
authors: Ameziane
authors: Department of Pathology, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: Carolien H M
authors: CH
authors: van Deurzen
authors: Division of Molecular Pathology, Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Petra
authors: P
authors: Ter Brugge
authors: Department of Toxicogenetics, Leiden University Medical Center, Leiden, the Netherlands.
authors: Matty
authors: M
authors: Meijers
authors: Department of Medical Oncology, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: Anieta M
authors: AM
authors: Sieuwerts
authors: Department of Medical Oncology, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: John W
authors: JW
authors: Martens
authors: AstraZeneca, iMed Oncology, Macclesfield, Cheshire, United Kingdom.
authors: Mark J
authors: MJ
authors: O'Connor
authors: Department of Toxicogenetics, Leiden University Medical Center, Leiden, the Netherlands.
authors: Harry
authors: H
authors: Vrieling
authors: Department of Genetics, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: Jan H J
authors: JH
authors: Hoeijmakers
authors: Division of Molecular Pathology, Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Jos
authors: J
authors: Jonkers
authors: Department of Genetics, Erasmus University Medical Center, Rotterdam, the Netherlands. Cancer Genomics Center Netherlands, Erasmus University Medical Center, Rotterdam, the Netherlands. Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: Roland
authors: R
authors: Kanaar
authors: Department of Clinical Genetics, VU University Medical Center, Amsterdam, the Netherlands.
authors: Johan P
authors: JP
authors: de Winter
authors: Department of Toxicogenetics, Leiden University Medical Center, Leiden, the Netherlands. Department of Human Genetics, Leiden University Medical Center, Leiden, the Netherlands.
authors: Maaike P
authors: MP
authors: Vreeswijk
authors: Department of Medical Oncology, Erasmus University Medical Center, Rotterdam, the Netherlands.
authors: Agnes
authors: A
authors: Jager
authors: Department of Genetics, Erasmus University Medical Center, Rotterdam, the Netherlands. d.vangent@erasmusmc.nl.
authors: Dik C
authors: DC
authors: van Gent
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001681:Biological Assay / Q000379:methods*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005455:Fluorescent Antibody Technique; D019398:Genes, BRCA1; D024522:Genes, BRCA2; D059765:Homologous Recombination / Q000528:radiation effects*; D006801:Humans; D051379:Mice; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D051135:Rad51 Recombinase / Q000528:radiation effects*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C495153:RAD51 protein, human; D051135:Rad51 Recombinase