Current applications of molecular testing on body cavity fluids

Our plain-English summary of Current applications of molecular testing on body cavity fluids, by D. Pinto, F. Schmitt (Diagnostic Cytopathology, 2020).

The study

• Authors: D. Pinto, F. Schmitt
• Journal: Diagnostic Cytopathology
• Published: 2020;48(9):840-851
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: Effusion cytology has a high sensitivity for the diagnosis of malignancy and provides abundant material for molecular testing. Effusion draining is a minimally invasive procedure with few complications.

Materials And Methods: We performed a review of publications regarding the use of molecular testing in serous effusions.

Results: In diagnostics, BAP-1 IHC and CDKN2A FISH are powerful tools for the diagnosis of malignant mesothelioma. FISH, PCR, and EBER-ISH work well in lymphomas. RT-PCR may enhance the diagnosis of secondary epithelial malignancies. In theranostics, molecular testing on serous effusions is widely reported for the detection of alterations in genes related to lung carcinomas, such as EGFR, ALK, ROS1, and BRAF. PD-L1 expression testing by immunohistochemistry (IHC) also seems to be viable in this type of sample. HER2 FISH and IHC provide actionable results in the context of breast malignancies. Results in serous effusions seem to be equivalent to tissue biopsies for most applications and across different molecular techniques. The most interesting technology is next-generation sequencing (NGS), given its ability to sequence multiple genes on a single sample and the decreasing costs that have closely followed increasing throughputs. Cell-free DNA from effusion supernatants might be the most promising area for future research, showing superiority to serum and even to cell-block samples in limited studies.

Conclusions: Molecular tests are viable in serous effusion specimens when sufficient material is available. Given the rising importance of molecular testing we expect this to be an active field of research in the near future.

© 2020 Wiley Periodicals, Inc.

In plain English

This article was a literature review, not a new study of patients. The authors searched four databases for publications on molecular laboratory tests done on fluid drained from the linings of the chest, abdomen or heart (serous effusions). The review did not study asbestos exposure; it noted only that malignant mesothelioma usually arises in that context. For telling mesothelioma apart from reactive (non-cancerous) lining cells, reviewed studies suggested BAP-1 protein loss is nearly 100% specific. Because melanomas and renal cell carcinomas can also lose BAP-1, the cells must first be shown to be mesothelial. They also suggested that homozygous CDKN2A deletion (loss of both gene copies), found in around 75% of mesotheliomas, is absent from reactive lining cells. The authors reported that combining BAP-1 staining with either MTAP staining or CDKN2A testing appeared more sensitive than any single test, without losing specificity. Across most applications, results in fluid samples seemed equivalent to tissue biopsies. The authors concluded that what matters is sample adequacy, not sample type. They noted that not every sample type has been fully validated for every genetic change.

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: Narrative literature review
• Who was studied: Published studies on molecular testing in serous effusions (pleural, pericardial and peritoneal fluid), found by searching four databases. The number of publications and the search dates were not stated.
• Exposure: Not an exposure study. The review covered molecular and related tests (immunohistochemistry, FISH, PCR, next-generation sequencing and others) on effusion samples. Asbestos was mentioned only as the usual background of malignant mesothelioma.
• Main results:
  • Recent studies reviewed suggested that loss of BAP-1 expression is nearly 100% specific for malignant mesothelioma. The article discusses this marker for distinguishing mesothelioma from benign mesothelial proliferations.
  • BAP-1 can also be lost in other tumors such as melanomas and renal cell carcinomas. The cells must therefore first be shown to be mesothelial (for example, calretinin-positive) before this marker is used.
  • Homozygous CDKN2A deletion was reported in around 75% of malignant mesotheliomas and as absent from reactive mesothelium.
  • Loss of MTAP expression was reported in over 70% of cases with CDKN2A deletion, making MTAP staining a possible substitute for CDKN2A FISH.
  • BAP-1 staining combined with either MTAP staining or CDKN2A FISH appeared more sensitive than any single method for diagnosing mesothelioma, without losing specificity.
  • Results in serous effusions seemed equivalent to tissue biopsies for most applications and across different molecular techniques.
  • One reviewed study included 48 cytology-tissue matched cases (bronchoalveolar lavage and serous effusion specimens). In specimens with less than 10% tumor cellularity, next-generation sequencing had a sensitivity over 80% versus 14% for direct sequencing.
  • In one reviewed study of 44 patients with high-grade serous ovarian carcinoma, BRCA mutation testing agreed 100% between cytology and tissue samples.
  • For lymphomas, the authors concluded that PCR and FISH are viable alternatives to flow cytometry for establishing monoclonality.
  • For epithelial cancers, the authors concluded that molecular techniques so far seem to offer little over immunohistochemistry for diagnosis.
• The authors' conclusion: The authors concluded that almost all molecular techniques seem to work in serous effusions with efficacies very similar to tissue biopsies, and that sample adequacy matters more than sample type.
• Limitations the authors state:
  • Not all sample types have been thoroughly validated for all mutations, deletions, translocations and fusions.
  • Most diagnostic studies on epithelial cancers in effusions were based on small retrospective cohorts.
  • Cytology-tissue equivalence for BRCA testing has not yet been shown for somatic mutations or for breast carcinomas.
  • The algorithmic approach to classifying lymphomas in effusions remains to be validated.
  • The authors did not recommend routine use of cell-free DNA testing from effusion supernatants.

Topics

Medical terms in this study, explained in our Lexicon: Molecular Profiling, Cytology, CDKN2A, Fluorescence In Situ Hybridization (FISH), Malignant Mesothelioma, Carcinoma, EGFR, ROS1.

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• Rapid and easy method for monitoring oxidative stress markers in body fluids of patients with asbestos or silica-induced lung diseases — K. Syslová, P. Kacer, et al. (2009)
• Preparation of extrapulmonary tissues and body fluids for quantitative transmission electron microscope analysis of asbestos and other mineral particle concentrations — P.M. Cook (1979)
• Vascular endothelial growth factor in pleural fluid for differential diagnosis of benign and malignant origin and its clinical applications — A. Fiorelli, G. Vicidomini, et al. (2011)
• Diagnostic use of muscle markers in the cytologic evaluation of serous fluids — A.M. Afify, B.M. Al-Khafaji, et al. (2002)

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