The importance of FISH signal cut-off values for 9p21 deletion in malignant pleural mesothelioma: Is it underestimated?

Our plain-English summary of The importance of FISH signal cut-off values for 9p21 deletion in malignant pleural mesothelioma: Is it underestimated?, by G. Kulduk, Ö. Ekinci, G. Toker, et al (Pathology, Research and Practice, 2019).

The study

• Authors: G. Kulduk, Ö. Ekinci, G. Toker, U. Demirci, E. Özaydın, N. Akyürek, L. Memiş
• Journal: Pathology, Research and Practice
• Published: 2019;215(6):152377
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant mesothelioma (MM) is an aggressive cancer with a poor prognosis. The most common genetic alteration in MM is the deletion of the INK4a/ARF locus, which encodes the p16 protein and is located on the short arm of chromosome 9 (9p21). Recently, it has been shown that homozygous deletion of 9p21 has both diagnostic and prognostic significance in MM. It is a known fact that, to interpret fluorescence in situ hybridization (FISH) signals, a cut-off value for each probe should be determined for a correct diagnosis. To our knowledge, there is no consensus or confirmed protocol for cut-off values to evaluate FISH signals in MMs. Therefore, the aim of our research was to address 9p21 deletion status and p16 expression profiles of MM by determining our own cut-off values and the effectiveness of using p16 negativity and 9p21 deletion as markers for differentiating MMs from benign mesothelial proliferations in 114 cases. We established a cut-off value for the detection of 9p21 deletion by using 13 benign reactive cases (6 reactive mesothelial hyperplasias and 7 chronic fibrinous pleuritis cases) and found between 0-7%. According to our calculations, homozygous deletion was defined by loss of both p16 gene signals in at least 13.3% of the nuclei that showed at least 1 signal for the CEP 9 probe. Our FISH results showed homozygous 9p21 deletion in 82 of the 114 cases of MM (71.9%), and p16 expression was negative in 75 of the 114 cases (65.8%). The correlation between loss of p16 protein expression and 9p21 deletion was statistically significant. Among the p16-negative cases, 86.7% also had the 9p21 deletion. The combined examination of the 9p21 deletion and loss of p16 expression is helpful for diagnostic purposes, but because the FISH method is an expensive technique and loss of p16 expression is not specific for mesotheliomas, p16 negativity can guide practitioners to eliminate cases that require further investigation by FISH. The variability in the significance of 9p21 homozygous deletion results from inconsistencies among different institutes, suggesting that each institute should establish its own cut-off value using reactive mesothelial proliferations. Alternatively, global studies are needed to assess cut-off values.

Copyright © 2019 Elsevier GmbH. All rights reserved.

In plain English

This study used archived tumor tissue to test a laboratory marker for diagnosing malignant mesothelioma. It did not report on asbestos exposure. The authors examined 114 patients with malignant mesothelioma from two hospitals in Turkey. All samples were pleural biopsies or surgical resections. Two tests were used: one looked for loss of both copies of a gene region called 9p21, the other for loss of the p16 protein. To decide how much gene loss counts as a true deletion, the authors measured 13 benign, non-cancer cases. They found deletion in 0 to 7% of cells, and from this set a threshold of 13.3% of cells. Using that threshold, 82 of 114 mesotheliomas (71.9%) showed the deletion, including all 7 sarcomatoid cases. The p16 protein was lost in 75 of 114 (65.8%). Of the 75 cases without p16, 65 (86.7%) also had the deletion. The authors concluded that each institute should set its own threshold using benign reactive mesothelial cases.

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: Laboratory study of archived tumor tissue (tissue microarrays) from patients already diagnosed with malignant mesothelioma, compared with benign reactive cases
• Who was studied: 114 patients with malignant mesothelioma: 74 diagnosed 2004 to 2014 at Gazi University and 40 diagnosed 2009 to 2014 at Atatürk Chest Diseases and Thoracic Surgery Education and Research Hospital, Turkey. There were 65 men and 49 women. All specimens were pleural biopsies or surgical resections. Tumor types were 74 epithelioid, 33 biphasic and 7 sarcomatoid. There were also 13 benign reactive cases (6 reactive mesothelial hyperplasias, 7 chronic fibrinous pleuritis).
• Main results:
  • In the 13 benign cases, deletion was seen in 0 to 7% of cells. The authors set the threshold for homozygous 9p21 deletion at loss of both p16 gene signals in at least 13.3% of qualifying cells.
  • 9p21 deletion was found in 82 of 114 mesothelioma cases (71.9%).
  • Homozygous deletion was found by tumor type: 44 of 74 epithelioid (59.5%), 31 of 33 biphasic (93.9%) and 7 of 7 sarcomatoid (100%). The link with tumor type was statistically significant.
  • Loss of p16 protein was found in 75 of 114 cases (65.8%): 38 of 74 epithelioid, 31 of 33 biphasic and 6 of 7 sarcomatoid.
  • Loss of p16 protein was significantly associated with 9p21 deletion. 65 of the 75 p16-negative cases (86.7%) had the homozygous deletion.
  • The reported sensitivity of loss of p16 protein was 74.5% and its specificity 50%. The authors reported 71.9% sensitivity and 100% specificity for 9p21 deletion.
  • p16 protein loss showed no statistically significant link with tumor stage (pT), lymph node involvement (N) or distant metastasis (M). 9p21 deletion also showed no significant link with pT, N or M.
• The authors' conclusion: The authors concluded that results vary between institutes. They suggested each institute should set its own threshold for 9p21 deletion using reactive (benign) mesothelial proliferations, or that global studies are needed.

Topics

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

Medical terms in this study, explained in our Lexicon: Fluorescence In Situ Hybridization (FISH), Pleural Mesothelioma, Mesothelioma, Prognosis, Homozygous Deletion, Reactive Mesothelial Hyperplasia.

Related studies

• 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)
• p16 FISH deletion in surface epithelial mesothelial proliferations is predictive of underlying invasive mesothelioma — H. Hwang, C. Tse, et al. (2014)
• Utility of BAP1 Immunohistochemistry and p16 (CDKN2A) FISH in the Diagnosis of Malignant Mesothelioma in Effusion Cytology Specimens — H.C. Hwang, B.S. Sheffield, et al. (2016)
• BAP1 Immunohistochemistry and p16 FISH in the Diagnosis of Sarcomatous and Desmoplastic Mesotheliomas — H.C. Hwang, S. Pyott, et al. (2016)
• FISH assay development for the detection of p16/CDKN2A deletion in malignant pleural mesothelioma — C.T. Chung, C. Santos Gda, et al. (2010)
• 9p21 deletion in the diagnosis of malignant mesothelioma, using fluorescence in situ hybridization analysis — M. Takeda, T. Kasai, et al. (2010)

Browse more research in Pathology, Research and Practice, or return to medical research.