Cytologic Differential Diagnosis of Malignant Mesothelioma and Reactive Mesothelial Cells With FISH Analysis of p16

Our plain-English summary of Cytologic Differential Diagnosis of Malignant Mesothelioma and Reactive Mesothelial Cells With FISH Analysis of p16, by K. Hiroshima, D. Wu, M. Hasegawa, et al (Diagnostic Cytopathology, 2016).

The study

• Authors: K. Hiroshima, D. Wu, M. Hasegawa, E. Koh, Y. Sekine, D. Ozaki, T. Yusa, A.E. Walts, A.M. Marchevsky, K. Nabeshima, Y. Tada, H. Shimada, M. Tagawa
• Journal: Diagnostic Cytopathology
• Published: 2016;44(7):591-8
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Mesothelioma patients often present with serosal effusions, which are ideal for cytopathological diagnoses. However, the morphological overlap between malignant and benign mesothelial proliferation can make a conclusive cytological diagnosis of mesothelioma elusive because immunohistochemical staining does not discriminate definitively between the two in this setting. p16 is deleted in up to 80% of pleural mesotheliomas. The aim of this study was to establish the correlation between the p16 deletion status of the cell block with that of its corresponding tumor using fluorescence in situ hybridization (FISH) analysis for individual patient tumors.

Methods: Twenty-two biopsies and 24 corresponding cell blocks, containing serosal effusions with atypical mesothelial cells from 22 patients with histologically confirmed pleural mesotheliomas, were analyzed with p16 FISH. Seventeen cell blocks consisting of serosal effusions with reactive mesothelial cells from nonmesothelioma cases were also analyzed. Combined immunofluorescence and FISH were also performed.

Results: Seventeen of the 22 mesothelioma patients (77.3%) showed homozygous deletions of p16 in the tumor tissue and in the atypical mesothelial cells from the cell blocks. p16 FISH followed by immunofluorescence with EMA was helpful towards identifying the mesothelioma cells in the cell blocks.

Conclusion: We confirmed that the p16 FISH results obtained from the cell blocks are as reliable as those from the tissue sections. Cell block analysis is recommended for patients with serosal effusions of unknown origins with the following methods: immunohistochemistry should be performed to validate the mesothelial origin, and p16 FISH should be performed to confirm malignancy. Diagn. Cytopathol. 2016;44:591-598. © 2016 Wiley Periodicals, Inc.

© 2016 Wiley Periodicals, Inc.

In plain English

In this laboratory study, the authors tested whether a genetic test called p16 FISH, which looks for loss of both copies of the p16 gene, gives the same result on fluid that collects around the lungs or in the abdomen (processed into 'cell blocks') as on tissue biopsies. They examined 22 biopsies and 24 cell blocks from 22 patients with confirmed pleural mesothelioma, plus 17 cell blocks from people without mesothelioma whose fluid held reactive, non-cancerous mesothelial cells. The reactive cells were used to set a cut-off: the deletion was called present when more than 15.0% of cells showed it. In reactive cells the figure ranged from 0 to 10.0%. Seventeen of the 22 mesothelioma patients (77.3%) showed the deletion in both tissue and cell blocks. Results from the two sample types agreed closely (R-squared 0.8091). Staining for a marker called EMA helped identify mesothelioma cells. The authors concluded that cell-block results are as reliable as tissue results. The study did not examine asbestos exposure.

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: Diagnostic laboratory study comparing p16 FISH results on effusion cell blocks with results on matching tumor biopsies, using cell blocks from patients without mesothelioma to set the cut-off value
• Who was studied: 22 patients with histologically confirmed pleural mesothelioma (20 male, 2 female; mean age 66.3 years; 15 epithelioid, 6 biphasic, 1 sarcomatoid), providing 22 biopsies and 24 cell blocks collected between 2005 and 2015. A comparison group of 17 cell blocks with reactive mesothelial cells came from patients without mesothelioma at the authors' institutions.
• Exposure: Not addressed. The study examined a diagnostic genetic marker (homozygous deletion of p16/CDKN2A) and did not report asbestos or other exposures.
• Main results:
  • In the mesothelioma patients, 17 of 22 (77.3%) showed homozygous deletion of p16 in both the tumor tissue and the atypical mesothelial cells in the cell blocks.
  • In the reactive (non-mesothelioma) cells, the homozygous deletion pattern appeared in 0 to 10.0% of nuclei (mean 3.65%, SD 2.85%). Based on this, the cell-block cut-off for homozygous deletion was set at more than 15.0% of nuclei.
  • In the mesothelioma patients, the percentage of cells showing the deletion pattern in tissue and in cell blocks agreed closely (coefficient of determination R-squared = 0.8091).
  • Of the 17 mesotheliomas with homozygous deletion, 11 showed the deletion pattern in more than 60% of analyzed cell-block cells. The 5 mesotheliomas without deletion showed the pattern in fewer than 10% of cells.
  • Large cell clusters were not seen in cell blocks with reactive mesothelial cells. In the mesothelioma patients, 11 of 22 (50.0%) cell blocks had large clusters.
  • Cell blocks from 17 of the 22 mesothelioma cases were EMA-positive. EMA was negative in 3 of the 17 (17.6%) with p16 deletion and in 2 of the 5 (40%) without deletion. When combined with FISH, EMA staining highlighted the mesothelioma cells being analyzed.
• The authors' conclusion: The authors concluded that p16 FISH results on cell blocks are as reliable as those on tissue sections. They recommended analyzing cell blocks from effusions of unknown origin with immunohistochemistry to confirm mesothelial origin and with p16 FISH to confirm malignancy.
• Limitations the authors state:
  • It is hard to call a deletion when the percentage of cells with it is only slightly above the cut-off. One benign case had the pattern in 10% of cells.
  • Cells without the deletion may be either mesothelioma cells or inflammatory cells, which are hard to tell apart under fluorescence microscopy.
  • Thin sections can cut through part of the cell nucleus, causing artificial signal loss.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Differential Diagnosis, Malignant Mesothelioma, Reactive Mesothelial Cells, Fluorescence In Situ Hybridization (FISH), Mesothelioma, Immunohistochemistry, Pleural Mesothelioma, Cell Block.

Related studies

• BAP1 Immunostain and CDKN2A (p16) FISH Analysis: Clinical Applicability for the Diagnosis of Malignant Mesothelioma in Effusions — A.E. Walts, K. Hiroshima, et al. (2016)
• Usefulness of p16/CDKN2A fluorescence in situ hybridization and BAP1 immunohistochemistry for the diagnosis of biphasic mesothelioma — D. Wu, K. Hiroshima, et al. (2017)
• Cytological differential diagnosis among adenocarcinoma, epithelial mesothelioma, and reactive mesothelial cells in serous effusions by immunocytochemistry — X.Y. Su, G.D. Li, et al. (2011)
• Diagnostic usefulness of p16/CDKN2A FISH in distinguishing between sarcomatoid mesothelioma and fibrous pleuritis — D. Wu, K. Hiroshima, et al. (2013)
• HEG1, BAP1, and MTAP are useful in cytologic diagnosis of malignant mesothelioma with effusion — K. Hiroshima, D. Wu, et al. (2021)
• Use of p16 FISH for differential diagnosis of mesothelioma in smear preparations — K. Nabeshima, S. Matsumoto, et al. (2016)

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