title: Genetic heterogeneity of single disseminated tumour cells in minimal residual cancer.
abstract: BACKGROUND
  Because cancer patients with small tumours often relapse despite local and systemic treatment, we investigated the genetic variation of the precursors of distant metastasis at the stage of minimal residual disease. Disseminated tumour cells can be detected by epithelial markers in mesenchymal tissues and represent targets for adjuvant therapies.
  
  
  METHODS
  We screened 525 bone-marrow, blood, and lymph-node samples from 474 patients with breast, prostate, and gastrointestinal cancers for single disseminated cancer cells by immunocytochemistry with epithelial-specific markers. 71 (14%) of the samples contained two or more tumour cells whose genomic organisation we studied by single cell genomic hybridisation. In addition, we tested whether TP53 was mutated. Hierarchical clustering algorithms were used to determine the degree of clonal relatedness of sister cells that were isolated from individual patients.
  
  
  RESULTS
  Irrespective of cancer type, we saw an unexpectedly high genetic divergence in minimal residual cancer, particularly at the level of chromosomal imbalances. Although few disseminated cells harboured TP53 mutations at this stage of disease, we also saw microheterogeneity of the TP53 genotype. The genetic heterogeneity was strikingly reduced with the emergence of clinically evident metastasis.
  
  
  CONCLUSIONS
  Although the heterogeneity of primary tumours has long been known, we show here that early disseminated cancer cells are genomically very unstable as well. Selection of clonally expanding cells leading to metastasis seems to occur after dissemination has taken place. Therefore, adjuvant therapies are confronted with an extremely large reservoir of variant cells from which resistant tumour cells can be selected.
authors.affiliation: Institut für Immunologie, Ludwig-Maximilians-Universität München, D-80336 München, Germany. christoph.klein@ifi.med.uni-muenchen.de
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Klein
authors.forename: Thomas J F
authors.initials: TJ
authors.lastname: Blankenstein
authors.forename: Oleg
authors.initials: O
authors.lastname: Schmidt-Kittler
authors.forename: Marco
authors.initials: M
authors.lastname: Petronio
authors.forename: Bernhard
authors.initials: B
authors.lastname: Polzer
authors.forename: Nikolas H
authors.initials: NH
authors.lastname: Stoecklein
authors.forename: Gert
authors.initials: G
authors.lastname: Riethmüller
mesh_terms: D001853:Bone Marrow / Q000473:pathology; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D017931:DNA Primers; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000235:genetics* / Q000473:pathology; D016158:Genes, p53 / Q000235:genetics; D018740:Genetic Heterogeneity; D006801:Humans; D008198:Lymph Nodes / Q000166:cytology; D008297:Male; D009362:Neoplasm Metastasis; D018365:Neoplasm, Residual / Q000235:genetics / Q000473:pathology; D009360:Neoplastic Cells, Circulating / Q000473:pathology; D016133:Polymerase Chain Reaction; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000473:pathology
chemical_list: D017931:DNA Primers