HEG1, BAP1, and MTAP are useful in cytologic diagnosis of malignant mesothelioma with effusion

Our plain-English summary of HEG1, BAP1, and MTAP are useful in cytologic diagnosis of malignant mesothelioma with effusion, by K. Hiroshima, D. Wu, S. Hamakawa, et al (Diagnostic Cytopathology, 2021).

The study

• Authors: K. Hiroshima, D. Wu, S. Hamakawa, S. Tsuruoka, D. Ozaki, H. Orikasa, M. Hasegawa, E. Koh, Y. Sekine, Y. Yonemori, K. Nabeshima, S. Tsuji, Y. Miyagi, K. Imai
• Journal: Diagnostic Cytopathology
• Published: 2021;49(5):622-632
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The specificity and sensitivity of HEG1 for malignant mesothelioma (MM) is high. The use of BAP1/MTAP immunohistochemistry (IHC) is recommended to separate benign and malignant mesothelial proliferations. We determined how ancillary techniques can be used for the cytological diagnosis of MM with effusion.

Methods: Cell blocks from effusions from cases with MM, reactive mesothelial cells (RMCs), and carcinomas were analyzed by IHC with HEG1, BAP1, and MTAP and with homozygous deletion (HD) of CDKN2A by fluorescence in situ hybridization. Staining scores were calculated for IHC by adding the number of categories for the staining intensity and the staining extension.

Results: HEG1 was positive in all (41/41) MMs, but negative in carcinomas, except for ovarian carcinomas. Overall 76.9% (20/26) of RMCs and 28.6% (6/21) of ovarian carcinomas expressed HEG1. BAP1 loss was found in 71.1% of MMs, but none was found in RMCs. MTAP loss was found in 76.2% of MMs, but none was found in RMCs. 73.9% of MMs harbored HD of CDKN2A. There was concordance between loss of MTAP and HD of CDKN2A in 95% of MMs.

Conclusion: HEG1 is a good marker for mesothelial differentiation in effusion cytology. HD of CDKN2A is frequently observed in cell blocks from effusions of MMs, and MTAP IHC may act as a surrogate for HD of CDKN2A. Cell block analysis is recommended for effusions of unknown origins with the following methods: IHC with HEG1 and claudin 4 to validate the mesothelial origin, followed by BAP1 and MTAP IHC to confirm malignancy.

© 2020 Wiley Periodicals LLC.

In plain English

This Japanese study tested laboratory stains and a gene test for diagnosing malignant mesothelioma from fluid (effusion) samples. The authors examined archived samples from 153 cases (2005 to 2019), including 62 mesotheliomas, 54 carcinomas and 36 with reactive, non-cancerous mesothelial cells. The marker HEG1 stained all 41 mesotheliomas tested. It stained no lung carcinomas (0 of 26), 6 of 21 ovarian carcinomas and 20 of 26 reactive-cell cases. Loss of BAP1 was found in 32 of 45 mesotheliomas and 0 of 9 reactive-cell cases. Loss of MTAP was found in 16 of 21 mesotheliomas and 0 of 5 reactive-cell cases. Homozygous deletion of the CDKN2A gene (both copies lost) was found in 34 of 46 mesotheliomas and 0 of 8 reactive-cell cases. MTAP results matched the gene test in 19 of 20 mesotheliomas. The authors noted that HEG1 alone made mesothelioma hard to tell apart from florid reactive-cell growth. They concluded that MTAP staining may substitute for the gene test. They recommended HEG1 and claudin 4 staining, then BAP1 and MTAP staining, and the gene test if neither shows loss. Asbestos exposure was not studied.

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 laboratory study of archived effusion cell blocks, using immunohistochemistry (staining) and fluorescence in situ hybridization (FISH, a gene test)
• Who was studied: 153 effusion cases from Tokyo Women's Medical University Yachiyo Medical Center, Chiba Rosai Hospital, Saitama Medical Center and Showa General Hospital in Japan, 2005 to 2019. The cases were 62 malignant mesotheliomas (24 epithelioid, 9 biphasic, 29 not otherwise specified), 26 lung carcinomas, 21 ovarian carcinomas, 7 other carcinomas, 1 angiosarcoma and 36 cases with reactive mesothelial cells. Of the 62 mesotheliomas, 33 were confirmed by biopsy and 29 were diagnosed from clinical findings and cytology.
• Exposure: Asbestos exposure was not studied. The study tested diagnostic markers: HEG1, BAP1 and MTAP staining, and FISH for homozygous deletion of the CDKN2A gene. BAP1, MTAP and FISH testing was done only in mesotheliomas and reactive-cell cases.
• Main results:
  • HEG1 staining was positive in all 41 mesotheliomas tested (41/41).
  • HEG1 was not expressed in the 26 lung carcinomas or the 7 other carcinomas.
  • HEG1 was expressed in 6 of 21 ovarian carcinomas (28.6%), all of them serous carcinomas. It was also expressed in 20 of 26 reactive mesothelial cell cases (76.9%).
  • Among malignant cytology specimens, a HEG1 staining-score cutoff of 5 gave the highest accuracy for diagnosing mesothelioma: 97.9%.
  • BAP1 loss was found in 32 of 45 mesotheliomas (71.1%) and in none of the 9 reactive mesothelial cell cases tested (0/9).
  • MTAP loss was found in 16 of 21 mesotheliomas (76.2%) and in none of the 5 reactive mesothelial cell cases tested (0/5).
  • Homozygous deletion of CDKN2A was found by FISH in 34 of 46 mesotheliomas (73.9%) and in none of the 8 reactive mesothelial cell effusions tested.
  • In mesotheliomas, MTAP loss agreed with homozygous CDKN2A deletion in 19 of 20 cases (95.0%). MTAP had a sensitivity of 94.1% and a specificity of 100% for the FISH result. No relationship was found between BAP1 loss and CDKN2A deletion.
  • Of 47 mesotheliomas tested by BAP1, MTAP and/or FISH, 43 (91.5%) showed at least one abnormality. In reactive mesothelial cell cases the figure was 0 of 9 (Table 4).
  • The traditional mesothelial markers were positive in mesotheliomas as follows: calretinin 92.3% (36/39), WT1 94.7% (36/38) and podoplanin 92.7% (38/41). Each was positive in 100% (20/20) of reactive mesothelial cell cases.
• The authors' conclusion: The authors concluded that HEG1 is a good marker of mesothelial origin in effusions, although most reactive mesothelial cells also expressed it. MTAP staining may act as a surrogate for CDKN2A FISH. The authors recommended cell block analysis for effusions of unknown origin in steps: HEG1 and claudin 4 staining to validate mesothelial origin, then BAP1 and MTAP staining to confirm malignancy, with CDKN2A FISH when neither BAP1 nor MTAP is lost.
• Limitations the authors state:
  • Different numbers of cases were analyzed with each method, because only leftover archived material was available.
  • The mesothelioma samples almost all represented the epithelioid component. Poorly differentiated epithelioid types were not included, which the authors say may explain the higher marker expression they found.
  • HEG1 staining alone made it difficult to distinguish mesothelioma cells from florid proliferation of reactive mesothelial cells.

Topics

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

Medical terms in this study, explained in our Lexicon: HEG1, BAP1, MTAP, Malignant Mesothelioma, Immunohistochemistry, Cell Block, Reactive Mesothelial Cells, Carcinoma.

Related studies

• A combination of MTAP and BAP1 immunohistochemistry in pleural effusion cytology for the diagnosis of mesothelioma — Y. Kinoshita, T. Hida, et al. (2018)
• Loss of expression of BAP1 is a useful adjunct, which strongly supports the diagnosis of mesothelioma in effusion cytology — J. Andrici, A. Sheen, et al. (2015)
• Membranous HEG1 expression is a useful marker in the differential diagnosis of epithelioid and biphasic malignant mesothelioma versus carcinomas — K. Hiroshima, D. Wu, et al. (2021)
• Usefulness of methylthioadenosine phosphorylase and BRCA-associated protein 1 immunohistochemistry in the diagnosis of malignant mesothelioma in effusion cytology specimens — K.B. Berg, A.M. Churg, et al. (2020)
• A combination of MTAP and BAP1 immunohistochemistry is effective for distinguishing sarcomatoid mesothelioma from fibrous pleuritis — Y. Kinoshita, M. Hamasaki, et al. (2018)
• Usefulness of p16/CDKN2A fluorescence in situ hybridization and BAP1 immunohistochemistry for the diagnosis of biphasic mesothelioma — D. Wu, K. Hiroshima, et al. (2017)

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