Frequency of false-positive FISH 1p/19q codeletion in adult diffuse astrocytic gliomas

Matthew K. Ball, Thomas M. Kollmeyer, Corinne E. Praska, Michelle L. McKenna, Caterina Giannini, Aditya Raghunathan, Mark E. Jentoft, Daniel H. Lachance, Benjamin R. Kipp, Robert B. Jenkins, Cristiane M. Ida

Research output: Contribution to journalArticlepeer-review


Background: Oligodendroglioma is genetically defined by concomitant IDH (IDH1/IDH2) mutation and whole-arm 1p/19q codeletion. Codeletion of 1p/19q traditionally evaluated by fluorescence in situ hybridization (FISH) cannot distinguish partial from whole-arm 1p/19q codeletion. Partial 1p/19q codeletion called positive by FISH is diagnostically a "false-positive"result. Chromosomal microarray (CMA) discriminates partial from whole-arm 1p/19q codeletion. Herein, we aimed to estimate the frequency of partial 1p/19q codeletion that would lead to a false-positive FISH result. Methods: FISH 1p/19q codeletion test probe coordinates were mapped onto Oncoscan CMA data to determine the rate of partial 1p/19q codeletion predicted to be positive by FISH. Diffuse astrocytic gliomas with available CMA data (2015-2018) were evaluated and classified based on IDH1-R132H/ATRX/p53 immunohistochemistry, IDH/TERT promoter targeted sequencing, and/or CMA according to classification updates. Predicted false-positive cases were verified by FISH whenever possible. Results: The overall estimated false-positive FISH 1p/19q codeletion rate was 3.6% (8/223). Predicted false positives were verified by FISH in 6 (of 8) cases. False-positive rates did not differ significantly (P =. 49) between IDH-mutant (4.6%; 4/86) and IDH-wildtype (2.9%; 4/137) tumors. IDH-wildtype false positives were all WHO grade IV, whereas IDH-mutant false positives spanned WHO grades II-IV. Testing for 1p/19q codeletion would not have been indicated for most false positives based on current classification recommendations. Conclusion: Selective 1p/19q codeletion testing and cautious interpretation for conflicting FISH and histopathological findings are recommended to avoid potential misdiagnosis.

Original languageEnglish (US)
Article numbervdaa109
JournalNeuro-Oncology Advances
Issue number1
StatePublished - Jan 1 2020


  • WHO
  • astrocytoma
  • chromosomal microarray
  • oligodendroglioma

ASJC Scopus subject areas

  • Clinical Neurology
  • Oncology
  • Surgery


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