Low homozygous/high heterozygous deletion status by p16 FISH correlates with a better prognostic group than high homozygous deletion status in malignant pleural mesothelioma

Our plain-English summary of Low homozygous/high heterozygous deletion status by p16 FISH correlates with a better prognostic group than high homozygous deletion status in malignant pleural mesothelioma, by M. Hamasaki, S. Matsumoto, S. Abe, et al (Lung Cancer, 2016).

The study

• Authors: M. Hamasaki, S. Matsumoto, S. Abe, D. Hamatake, T. Kamei, K. Hiroshima, K. Kawahara, A. Sato, T. Tsujimura, Y. Nakatani, Y. Yoshida, A. Iwasaki, K. Nabeshima
• Journal: Lung Cancer
• Published: 2016;99:155-61
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Homozygous deletion (homo-d) of the p16 (CDKN2A) gene, as determined by fluorescence in situ hybridization (FISH), helps differentiate malignant pleural mesothelioma (MPM) from reactive mesothelial hyperplasia (RMH). Heterozygous deletion (hetero-d) has also been identified variably in p16 FISH. This study aimed to investigate the significance of homo-d and hetero-d of p16 in the diagnosis and prognosis of MPM.

Materials And Methods: p16 FISH was performed in 93 MPMs and 47 RMHs. Real-time polymerase chain reaction (PCR) and methylation specific PCR (MSP) were also performed for cases in which DNA was available. Overall survival (OS) was assessed via the Kaplan-Meier method and logrank test.

Results: Cutoff values for homo-d and hetero-d were set at 10% and 47%, respectively, based on p16 FISH results in RMH. In MPM, 80/93 (86.0%) were homo-d positive, and 15/93 (16.1%) were hetero-d positive. No RMH was homo/hetero-d positive. In nine cases of MPM with the low homo-d (<30%)/high hetero-d (>47%) pattern, FISH with a shorter probe caused a slight increase (from 20.1% to 26.5%) in the mean percentage of homo-d and a decrease in that of hetero-d (from 59.6% to 55.6%). Four cases in which the low homo-d/high hetero-d pattern was maintained with the shorter probe were further analyzed by real-time PCR, which separated them into a two (n=2) or one allele deletion group (n=2). MSP revealed no promoter methylation in the two cases with one allele deletion. The OS was significantly shorter in homo-d positive cases (n=24) than homo-d negative cases (n=5, p=0.0002) in the 29 MPM cases with follow-up data. Also, low homo-d/high hetero-d cases (n=5) had a significantly better prognosis than high homo-d (≥30%) cases (n=17, p=0.011).

Conclusions: Within p16 homo-d positive MPMs with poorer prognosis, the low homo-d/high hetero-d pattern may belong to a better prognostic subgroup in homo-d positive MPMs.

Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

In plain English

This Japanese laboratory study asked whether loss of the p16 (CDKN2A) gene, measured with a tissue test called FISH, helps tell malignant pleural mesothelioma apart from a benign condition, reactive mesothelial hyperplasia, and whether it relates to survival. The authors tested tissue from 93 mesothelioma patients and 47 hyperplasia patients from the pathology files of Fukuoka University Hospital. The article does not report asbestos exposure. Using cutoffs based on the benign samples, 80 of 93 mesotheliomas (86.0%) showed loss of both gene copies (homozygous deletion). None of the benign samples showed p16 deletions. Among 29 mesothelioma patients with follow-up, survival was significantly shorter in the 24 with homozygous deletion than in the 5 without it (p = 0.0002). Among patients with homozygous deletion, the 5 whose FISH result showed a low homozygous level (under 30% of cells) with a high heterozygous-deletion pattern survived significantly longer than the 17 with higher homozygous levels (p = 0.011). The authors concluded that this pattern may mark a group with better prognosis but that this needs confirmation in a larger cohort.

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 tissue samples taken from a hospital pathology file. The authors used FISH, real-time PCR and methylation-specific PCR, and analysed survival in a subset of patients.
• Who was studied: 93 patients with malignant pleural mesothelioma (79 male, 14 female; mean age 66.9 years, range 44 to 86) and 47 patients with reactive mesothelial hyperplasia (46 male, 1 female; mean age 31.5 years, range 16 to 78), at Fukuoka University Hospital, Japan. Survival data were available for 29 of the mesothelioma patients.
• Exposure: Asbestos exposure was not studied or reported. The factor examined was deletion of the p16 (CDKN2A) gene in tissue: loss of both copies (homozygous) or of one copy (heterozygous).
• Main results:
  • Cutoffs were derived from the reactive mesothelial hyperplasia samples (mean plus 3 standard deviations): 10% or more of cells for homozygous deletion and more than 47% for heterozygous deletion.
  • In the main text, of the 93 mesothelioma patients, 80 (86.0%) were positive for homozygous deletion and 14 (15.1%) for heterozygous deletion. The article's abstract gives 15/93 (16.1%) for heterozygous deletion.
  • None of the 47 reactive mesothelial hyperplasia patients had p16 deletions.
  • In mesotheliomas with the low homozygous / high heterozygous pattern (seven cases in the main text, nine in the abstract), the shorter GSP probe raised the mean percentage of homozygous deletion from 20.1% to 26.5% and lowered the mean percentage of heterozygous deletion from 59.6% to 55.6%.
  • Four patients kept the low homozygous / high heterozygous FISH pattern and had DNA available. Real-time PCR showed a two-copy deletion in two of them and a one-copy deletion in the other two.
  • The two patients with a one-copy deletion showed no methylation of the p16 promoter region.
  • Among the 29 mesothelioma patients with follow-up, overall survival was significantly shorter in the 24 with homozygous deletion than in the 5 without it (p = 0.0002).
  • Among patients with homozygous deletion, survival did not differ significantly between those whose heterozygous percentage exceeded their homozygous percentage and those where the reverse held (p = 0.130).
  • Patients with the low homozygous (under 30%) / high heterozygous FISH pattern (n = 5) had significantly better survival than patients with homozygous deletion of 30% or more (n = 17), p = 0.011. A very high homozygous level (90% or more) did not affect survival.
• The authors' conclusion: The authors concluded that the low homozygous / high heterozygous p16 deletion pattern may distinguish mesotheliomas with better prognosis from those with higher homozygous deletion levels, but that this needs confirmation in a larger cohort.
• Limitations the authors state:
  • The finding on the low homozygous / high heterozygous pattern needs confirmation in a larger cohort.
  • False positivity could not be completely ruled out for the cases classed as one-copy deletions.
  • Real-time PCR is of limited value when pure tumor cells cannot be obtained.
  • Longer FISH probes may produce small signals that mimic heterozygous deletion, especially when the deletion is small.

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), Homozygous Deletion, Pleural Mesothelioma, CDKN2A, Reactive Mesothelial Hyperplasia, Prognosis, Overall Survival.

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)
• FISH assay development for the detection of p16/CDKN2A deletion in malignant pleural mesothelioma — C.T. Chung, C. Santos Gda, et al. (2010)
• 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)
• 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)
• Homozygous deletion of CDKN2A/2B is a hallmark of iron-induced high-grade rat mesothelioma — Q. Hu, S. Akatsuka, et al. (2010)
• Use of p16 FISH for differential diagnosis of mesothelioma in smear preparations — K. Nabeshima, S. Matsumoto, et al. (2016)

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