Fluorescence in situ hybridization detection of chromosome 22 monosomy in pleural effusion cytology for the diagnosis of mesothelioma

Our plain-English summary of Fluorescence in situ hybridization detection of chromosome 22 monosomy in pleural effusion cytology for the diagnosis of mesothelioma, by Y. Kinoshita, M. Hamasaki, S. Matsumoto, et al (Cancer Cytopathology, 2021).

The study

• Authors: Y. Kinoshita, M. Hamasaki, S. Matsumoto, M. Yoshimura, A. Sato, T. Tsujimura, T. Kamei, K. Kawahara, A. Iwasaki, K. Nabeshima
• Journal: Cancer Cytopathology
• Published: 2021;129(7):526-536
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Malignant pleural mesothelioma (MPM) is characterized by mutations in several genes, including cyclin-dependent kinase-inhibitor 2A/p16 in the 9p21 locus, BRCA1-associated protein 1 (BAP1), and neurofibromatosis type 2 (NF2) in the 22q12 locus. Recent studies indicate that fluorescence in situ hybridization (FISH) detects hemizygous loss of NF2 in tissue specimens of MPM. The authors investigated whether NF2 FISH, either alone or in combination with other diagnostic assays (9p21 FISH, methylthioadenosine phosphorylase [MTAP] immunohistochemistry [IHC], and BAP1 IHC), effectively distinguishes MPM cells from reactive mesothelial cells (RMCs) in cell blocks prepared from pleural effusions.

Methods: FISH assays were used to examine the deletion status of NF2 and 9p21, and IHC was used to determine the expression of MTAP and BAP1 in cell blocks from 54 cases with MPM and 18 cases with RMCs.

Results: Hemizygous NF2 loss (chromosome 22 monosomy or hemizygous deletion) showed 51.9% sensitivity (48.1% for chromosome 22 monosomy and 3.7% for hemizygous deletion) and 100% specificity in differentiating MPM cells from RMCs. Combinations of NF2 FISH, 9p21 FISH, and BAP1 IHC assays yielded greater sensitivity (98.1%) than any assay alone (9p21 FISH, 61.1%; MTAP IHC, 52.8%; or BAP1 IHC, 60.4%). The level of hemizygous NF2 loss in cell blocks positively correlated with that in corresponding tissues. Furthermore, to overcome cytologic specimen-specific challenges, FISH combined with cytokeratin AE1/AE3 immunofluorescence was necessary in 25.9% of MPM cases for FISH assessment of predominantly scattered MPM cells.

Conclusions: NF2 FISH alone or in combination with other diagnostic assays effectively differentiates MPM cells from RMCs in cell blocks prepared from pleural effusions.

© 2021 American Cancer Society.

In plain English

This retrospective study from Japan tested whether a test called NF2 FISH could tell malignant pleural mesothelioma cells apart from non-cancerous reactive mesothelial cells in fluid collected from around the lungs (pleural effusions). NF2 FISH looks for loss of the NF2 gene region on chromosome 22. The authors examined cell samples from 54 mesothelioma cases and 18 reactive cases taken from pathology files at Fukuoka University Hospital from 2010 to 2019. The study did not examine asbestos exposure. NF2 loss was found in 28 of the 54 mesothelioma cases (51.9%) and in none of the reactive cases. Three other tests, used alone, detected 52.8% to 61.1% of the mesothelioma cases. Combining NF2 FISH with 9p21 FISH and BAP1 staining detected 98.1%. No test or combination flagged any reactive case. NF2 results in fluid samples correlated with results in matching tissue. The authors concluded that NF2 FISH combined with other tests was effective for this distinction. They noted that the study was retrospective and small and that 13 cases were excluded for too few cells.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective diagnostic accuracy study of archived pleural effusion cell blocks
• Who was studied: Cell blocks from pleural effusions of 54 malignant pleural mesothelioma (MPM) cases (46 men, 8 women, mean age 71.5 years) and 18 reactive mesothelial cell (RMC) cases (10 men, 8 women, mean age 71.1 years), from the pleural lesion files of Fukuoka University Hospital, Japan, 2010 to 2019. This was after 7 MPM and 6 RMC cases were excluded for too few mesothelial cells.
• Exposure: Not an asbestos exposure study; patients' asbestos exposure was not reported. The tests examined were NF2 FISH, 9p21 FISH, MTAP immunohistochemistry and BAP1 immunohistochemistry.
• Main results:
  • NF2 FISH found hemizygous NF2 loss in 28 of 54 MPM cases (51.9%). This was chromosome 22 monosomy in 26 of 54 (48.1%) and hemizygous deletion in 2 of 54 (3.7%).
  • No RMC case showed hemizygous NF2 loss.
  • Specificity of every assay was 100%. Sensitivity for MPM was 51.9% for NF2 FISH, 61.1% for 9p21 FISH, 52.8% for MTAP IHC and 60.4% for BAP1 IHC. For MTAP IHC and BAP1 IHC, one mesothelioma case each was excluded from the calculation.
  • Combined sensitivities for MPM were 87% for BAP1 IHC with 9p21 FISH and 83.3% for BAP1 with MTAP IHC. The triple combination of NF2 FISH, 9p21 FISH and BAP1 IHC reached 98.1%.
  • In MPM cases, hemizygous NF2 loss was not statistically associated with homozygous 9p21 deletion (P = .586), MTAP loss (P = 1.00) or BAP1 loss (P = 1.00).
  • In MPM cases with corresponding tissue specimens (n = 18 in Figure 6), the percentage of cells with hemizygous NF2 loss in cell blocks correlated positively with that in tissue (r = 0.834; P < .001).
  • FISH combined with cytokeratin AE1/AE3 immunofluorescence was needed to assess scattered cells in 14 MPM cases (25.9%) and 7 RMC cases (38.9%).
• The authors' conclusion: The authors concluded that NF2 FISH combined with other diagnostic assays was effective for distinguishing MPM from RMC in cell blocks from pleural effusions. They stated that NF2 FISH alone had insufficient sensitivity compared with 9p21 FISH and BAP1 IHC, and that the combination approach needs validation in a larger cohort.
• Limitations the authors state:
  • Retrospective design with a relatively small number of patients
  • 13 cases were excluded because they had too few mesothelial cells
  • The cutoff for chromosome 22 monosomy was relatively high (47.1%), so enough cells must be counted to avoid misjudgment
  • BAP1 and MTAP IHC are not always straightforward to assess; one case each was indeterminate
  • Some samples were old, dating back to 2010. The authors state that internal control cells supported the reliability of FISH in these samples.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Fluorescence In Situ Hybridization (FISH), Pleural Effusion, Cytology, Mesothelioma, Pleural Mesothelioma, BAP1, MTAP, Immunohistochemistry.

Related studies

• Hemizygous loss of NF2 detected by fluorescence in situ hybridization is useful for the diagnosis of malignant pleural mesothelioma — Y. Kinoshita, M. Hamasaki, et al. (2020)
• Fluorescence in situ hybridization (FISH) provides estimates of minute and interstitial BAP1, CDKN2A, and NF2 gene deletions in peritoneal mesothelioma — S. Brich, F. Bozzi, et al. (2020)
• Usefulness of p16/CDKN2A fluorescence in situ hybridization and BAP1 immunohistochemistry for the diagnosis of biphasic mesothelioma — D. Wu, K. Hiroshima, et al. (2017)
• Fluorescence in situ hybridization in the definitive diagnosis of malignant mesothelioma in effusion cytology — S. Savic, N. Franco, et al. (2010)
• A combination of MTAP and BAP1 immunohistochemistry in pleural effusion cytology for the diagnosis of mesothelioma — Y. Kinoshita, T. Hida, et al. (2018)
• BAP1 immunohistochemistry has limited prognostic utility as a complement of CDKN2A (p16) fluorescence in situ hybridization in malignant pleural mesothelioma — S.M. McGregor, J. McElherne, et al. (2017)

Browse more research in Cancer Cytopathology, or return to medical research.