P14/ARF-Positive Malignant Pleural Mesothelioma: A Phenotype With Distinct Immune Microenvironment

Our plain-English summary of P14/ARF-Positive Malignant Pleural Mesothelioma: A Phenotype With Distinct Immune Microenvironment, by F. Pezzuto, F. Lunardi, L. Vedovelli, et al (Frontiers in Oncology, 2021).

The study

• Authors: F. Pezzuto, F. Lunardi, L. Vedovelli, F. Fortarezza, L. Urso, F. Grosso, G.L. Ceresoli, I. Kern, G. Vlacic, E. Faccioli, M. Schiavon, D. Gregori, F. Rea, G. Pasello, F. Calabrese
• Journal: Frontiers in Oncology
• Published: 2021;11:653497
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Introduction: The CDKN2A gene plays a central role in the pathogenesis of malignant pleural mesothelioma (MPM). The gene encodes for two tumor suppressor proteins, p16/INK4A and p14/ARF, frequently lost in MPM tumors. The exact role of p14/ARF in MPM and overall its correlation with the immune microenvironment is unknown. We aimed to determine whether there is a relationship between p14/ARF expression, tumor morphological features, and the inflammatory tumor microenvironment.

Methods: Diagnostic biopsies from 76 chemo-naive MPMs were evaluated. Pathological assessments of histotype, necrosis, inflammation, grading, and mitosis were performed. We evaluated p14/ARF, PD-L1 (tumor proportion score, TPS), and Ki-67 (percentage) by immunohistochemistry. Inflammatory cell components (CD3+, CD4+, CD8+ T lymphocytes; CD20+ B-lymphocytes; CD68+ and CD163+ macrophages) were quantified as percentages of positive cells, distinguishing between intratumoral and peritumoral areas. The expression of p14/ARF was associated with several clinical and pathological characteristics. A random forest-based machine-learning algorithm (Boruta) was implemented to identify which variables were associated with p14/ARF expression.

Results: p14/ARF was evaluated in 68 patients who had a sufficient number of tumor cells. Strong positivity was detected in 14 patients (21%) (11 epithelioid and 3 biphasic MPMs). At univariate analysis, p14/ARF-positive epithelioid mesotheliomas showed higher nuclear grade (G3) (p = 0.023) and higher PD-L1 expression (≥50%) (p = 0.042). The percentages of CD4 and CD163 in peritumoral areas were respectively higher and lower in p14/ARF positive tumors but did not reach statistical significance with our sample size (both p = 0.066). The Boruta algorithm confirmed the predictive value of PD-L1 percentage for p14/ARF expression in all histotypes.

Conclusions: p14/ARF-positive epithelioid mesotheliomas may mark a more aggressive pathological phenotype (higher nuclear grade and PD-L1 expression). Considering the results regarding the tumor immune microenvironment, p14/ARF-negative tumors seem to have an immune microenvironment less sensitive to immune checkpoint inhibitors, being associated with low PD-L1 and CD4 expression, and high CD163 percentage. The association between p14/ARF-positive MPMs and PD-L1 expression suggests a possible interaction of the two pathways. Confirmation of our preliminary results could be important for patient selection and recruitment in future clinical trials with anticancer immunotherapy.

Copyright © 2021 Pezzuto, Lunardi, Vedovelli, Fortarezza, Urso, Grosso, Ceresoli, Kern, Vlacic, Faccioli, Schiavon, Gregori, Rea, Pasello and Calabrese.

In plain English

This study examined tumor biopsies taken before any chemotherapy from 76 patients with malignant pleural mesothelioma, gathered at three Italian centers and one Slovenian center from 2011 to 2019. The authors stained the tissue for p14/ARF, a protein made by the CDKN2A gene, and compared it with tumor features and with immune cells in and around the tumor. A history of asbestos exposure was reported for 62% of patients and listed separately for the p14/ARF-positive and p14/ARF-negative groups, but no statistical test of exposure was reported. p14/ARF could be assessed in 68 samples and was strongly positive in 14 (21%), 11 of them epithelioid. Across all tumor types, high PD-L1 (50% or more of tumor cells) was linked with p14/ARF positivity (p = 0.015). Among epithelioid tumors, positivity was linked with higher nuclear grade. Differences in two immune cell types around the tumor were not statistically significant. Survival did not differ significantly between the groups. The authors concluded that p14/ARF-positive epithelioid tumors may mark a more aggressive phenotype, and called their results preliminary. They noted that the small sample may have left the study underpowered.

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 study of diagnostic biopsies, using pathology review and immunohistochemistry (tissue staining), with statistical comparison of p14/ARF-positive and p14/ARF-negative tumors
• Who was studied: 76 chemotherapy-naive patients with malignant pleural mesothelioma from three Italian centers and one Slovenian center, 2011 to 2019. p14/ARF was evaluable in 68 (89%) samples. Of these 68 patients, 51 (75%) were male and the median age was 72. Tumors were 47 epithelioid, 17 biphasic and 4 sarcomatoid.
• Exposure: Asbestos exposure was not the main variable studied. A positive history of asbestos exposure was obtained from 62% of patients. Table 1 lists exposure history separately for the p14/ARF-positive and p14/ARF-negative groups, with no statistical test. No fiber types, jobs or doses are reported. The factor compared was p14/ARF protein expression in tumor tissue.
• Main results:
  • p14/ARF was strongly positive in 14 of 68 evaluable patients (21%): 11 epithelioid and 3 biphasic. Loss of p14/ARF staining was seen in 54 cases (79%).
  • Across all histotypes, p14/ARF positivity was significantly associated with high PD-L1 expression in tumor cells (p = 0.015). PD-L1 of 50% or more was found in 7 of 14 (50%) p14/ARF-positive tumors and in 10 of 54 (18.5%) p14/ARF-negative tumors (Table 2). The Boruta machine-learning analysis also identified PD-L1 as a predictor.
  • Among epithelioid mesotheliomas, p14/ARF-positive tumors showed higher nuclear grade (G3) (p = 0.023) and higher PD-L1 expression (p = 0.042). In the Boruta analysis for this group, nuclear grade and PD-L1 were the two most important variables, although significance was not achieved.
  • In areas around the tumor, CD4 cells were higher and CD163 cells were lower in p14/ARF-positive tumors. Medians were 20.0% vs 2.5% for CD4 and 45.0% vs 70.0% for CD163. These differences were not statistically significant (both p = 0.066).
  • Median overall survival did not differ significantly: 9.3 months in p14/ARF-positive patients vs 9.8 months in p14/ARF-negative patients. Restricted mean survival time at 6 and 12 months also showed no differences.
• The authors' conclusion: The authors concluded that p14/ARF-positive epithelioid mesotheliomas may mark a more aggressive pathological phenotype, with higher nuclear grade and PD-L1 expression. They suggested the p14/ARF and PD-L1 pathways may interact. They described the results as preliminary and needing confirmation before use in selecting patients for immunotherapy trials.
• Limitations the authors state:
  • Small sample size; the study could be underpowered.
  • There is no standard definition of p14/ARF positivity. The lack of a cut-off value may influence how many samples are found positive.
  • PD-L1 evaluation is not standardized in mesothelioma, in terms of antibody clones, method of evaluation or threshold.
  • The molecular basis of the PD-L1 and p14/ARF association remains unknown.
  • The small and unequal sizes of the two groups did not allow a clear evaluation of the survival curves.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, CDKN2A, Tumor Microenvironment, Necrosis, Inflammation, PD-L1, Ki-67, Immunohistochemistry.

Related studies

• Unraveling tumor microenvironment heterogeneity in malignant pleural mesothelioma identifies biologically distinct immune subtypes enabling prognosis determination — K. Yang, T. Yang, et al. (2022)
• Cytotoxic T Cells in PD-L1-Positive Malignant Pleural Mesotheliomas Are Counterbalanced by Distinct Immunosuppressive Factors — M.M. Awad, R.E. Jones, et al. (2016)
• Spatially-resolved analyses of muscle invasive bladder cancer microenvironment unveil a distinct fibroblast cluster associated with prognosis — C. Feng, Y. Wang, et al. (2024)
• The epithelioid BAP1-negative and p16-positive phenotype predicts prolonged survival in pleural mesothelioma — A. Chou, C.W. Toon, et al. (2018)
• Molecular and Histopathological Characterization of the Tumor Immune Microenvironment in Advanced Stage of Malignant Pleural Mesothelioma — N.S. Patil, L. Righi, et al. (2018)
• Tumor Immune Microenvironment and Genetic Alterations in Mesothelioma — S. Hiltbrunner, L. Mannarino, et al. (2021)

Browse more research in Frontiers in Oncology, or return to medical research.