Use of p16 FISH for differential diagnosis of mesothelioma in smear preparations

Our plain-English summary of Use of p16 FISH for differential diagnosis of mesothelioma in smear preparations, by K. Nabeshima, S. Matsumoto, M. Hamasaki, et al (Diagnostic Cytopathology, 2016).

The study

• Authors: K. Nabeshima, S. Matsumoto, M. Hamasaki, T. Hida, T. Kamei, K. Hiroshima, T. Tsujimura, K. Kawahara
• Journal: Diagnostic Cytopathology
• Published: 2016;44(9):774-80
• Type of article: Review
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Because most of malignant pleural mesothelioma (MPM) patients first present with pleural effusion, detection of mesothelioma cells on effusion smears is critical for early diagnosis. Recently, accumulating evidence indicating that the cytological diagnosis of MPM supported by ancillary techniques is as reliable as that based on histopathology has led to new guidelines for the cytopathologic diagnosis of MPM. Based on the guidelines, a combination of cytomorphological criteria and verification by ancillary techniques is required for the cytologic diagnosis of MPM. Detection of p16 homozygous deletion by fluorescence in situ hybridization (FISH) is the most reliable ancillary technique for differentiating MPM from reactive mesothelial cells (RMC) because of its relatively high sensitivity and extremely high specificity. We showed that the p16 deletion status of MPM cells in pleural effusions reflected that of the underlying invasive MPM tissues, indicating the usefulness of p16 FISH in effusion smear cytology for MPM diagnosis. Thus, for differentiating MPM from RMC, we propose to perform p16 FISH as often as possible. A positive p16 homozygous deletion supports the diagnosis of MPM. However, a negative result does not rule out the possibility of MPM. In such cases, a morphological assessment is critical. Therefore, we analyzed the morphological characteristics of p16 deletion-positive mesothelioma cells using a combination of virtual microscopy and p16 FISH, and identified three morphological characteristics useful for the differentiation, including cell-in-cell engulfment with or without hump formation, multinucleate cells, and larger berry-like cell aggregates. Diagn. Cytopathol. 2016;44:774-780. © 2016 Wiley Periodicals, Inc.

© 2016 Wiley Periodicals, Inc.

In plain English

This review, by pathologists in Japan, examined p16 FISH, a laboratory test for telling malignant pleural mesothelioma (MPM) apart from reactive, non-cancerous mesothelial cells in fluid smears. It did not study asbestos exposure. Summarizing published studies, the authors reported loss of both copies of the p16 gene in a mean of 70% (range 60–93%) of MPM. This loss had never been reported in reactive mesothelial hyperplasia. The rate was lower in peritoneal mesothelioma (25–51%, mean 40%). The authors also described their own earlier study of epithelioid mesothelioma cases that had both smears and tissue. In it, every deletion-positive smear was also deletion-positive in the underlying tumor. Their earlier work also found three cell features significantly more often in deletion-positive mesothelioma cells than in reactive cells: cell-in-cell engulfment, multiple nuclei and larger clusters. The authors proposed a pathway for cases where cell appearance and staining suggest mesothelioma but cannot clearly separate it from reactive cells. In those cases, a positive result plus supporting clinical and radiologic evidence may allow diagnosis without biopsy. A negative result does not rule out MPM. In that case the authors called for assessing cell features, followed by tissue biopsy. The test cannot separate MPM from metastatic cancers.

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: Review (published as a 'Timely Review'), summarizing published p16 FISH studies and the authors' own earlier research
• Who was studied: Published p16 FISH data on mesothelioma and reactive mesothelial hyperplasia, compiled in Table I from studies dated 2003 to 2015. The review also covers the authors' own prior studies of pleural effusion smears and tissue from epithelioid mesothelioma cases in Japan.
• Exposure: Not studied. The review is about a diagnostic laboratory test (p16 FISH). It mentions only that MPM is associated with asbestos exposure; no fiber types or doses are discussed.
• Main results:
  • Across the published studies reviewed, p16 homozygous deletion was found in a mean of 70% (range 60–93%) of malignant pleural mesotheliomas
  • p16 homozygous deletion had never been reported in reactive mesothelial hyperplasia cases (100% specificity)
  • The deletion rate was 25–51% (mean 40%) in peritoneal mesotheliomas, compared with 60–90% (mean 70%) in MPM
  • For calling a sample deletion-positive, the authors' institution set a cutoff of more than 10% of nuclei showing the deletion pattern. The same cutoff applied to tissue sections and smears.
  • The authors' earlier study covered epithelioid mesothelioma cases with both effusion smears and tissue specimens. In those cases, all deletion-positive smears were also deletion-positive in the underlying MPM tissue.
  • In the authors' earlier study, three cell features were seen significantly more often in p16 deletion-positive MPM cells than in reactive mesothelial cells with a normal p16 pattern: cell-in-cell engulfment, multinucleate cells, and clusters of more than 10 cells
  • The authors suggested thresholds favoring MPM over reactive cells: cell-in-cell engulfment in more than 15% of cells (when more than 100 cells are examined), more than 25% binucleate cells, or more than 5% multinucleate cells
• The authors' conclusion: The authors proposed a diagnostic pathway for cases in which mesothelioma is suspected morphologically and immunocytochemically but is hard to distinguish from reactive mesothelial cells. In such cases, a p16 deletion-positive smear with supporting clinical and radiologic evidence may be sufficient to diagnose MPM without a tissue biopsy. A deletion-negative smear does not rule out MPM. It calls for a morphological assessment followed by tissue biopsy, as the IMIG guidelines suggest.
• Limitations the authors state:
  • p16 FISH cannot distinguish MPM from metastatic carcinomas or other tumors involving the pleura, because those tumors can also carry the deletion
  • Absence of the deletion does not mean a lesion is reactive, because some MPMs lack the deletion
  • Further studies with MPM and control groups are needed to make the cell-feature cutoff values more reliable

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), Differential Diagnosis, Mesothelioma, Pleural Mesothelioma, Pleural Effusion, Histopathology, Homozygous Deletion, Reactive Mesothelial Hyperplasia.

Related studies

• Deletion status of p16 in effusion smear preparation correlates with that of underlying malignant pleural mesothelioma tissue — T. Hida, S. Matsumoto, et al. (2015)
• Immunohistochemical detection of MTAP and BAP1 protein loss for mesothelioma diagnosis: Comparison with 9p21 FISH and BAP1 immunohistochemistry — T. Hida, M. Hamasaki, et al. (2017)
• p16/CDKN2A FISH in Differentiation of Diffuse Malignant Peritoneal Mesothelioma From Mesothelial Hyperplasia and Epithelial Ovarian Cancer — T. Ito, M. Hamasaki, et al. (2015)
• Low homozygous/high heterozygous deletion status by p16 FISH correlates with a better prognostic group than high homozygous deletion status in malignant pleural mesothelioma — M. Hamasaki, S. Matsumoto, et al. (2016)
• Fluorescence in situ hybridization detection of chromosome 22 monosomy in pleural effusion cytology for the diagnosis of mesothelioma — Y. Kinoshita, M. Hamasaki, et al. (2021)
• BAP1 immunohistochemistry and p16 FISH results in combination provide higher confidence in malignant pleural mesothelioma diagnosis: ROC analysis of the two tests — T. Hida, M. Hamasaki, et al. (2016)

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