External validation of pathological T adjustments in the ninth edition of the pleural mesothelioma tumor-node-metastasis classification

Our plain-English summary of External validation of pathological T adjustments in the ninth edition of the pleural mesothelioma tumor-node-metastasis classification, by Z. Liu, J. Cai, Y. Li, et al (Frontiers in Oncology, 2025).

The study

• Authors: Z. Liu, J. Cai, Y. Li, W. Weng
• Journal: Frontiers in Oncology
• Published: 2025;15:1557097
• Read it: PubMed · Publisher · Free full text

Abstract

Introduction: In the ninth edition pleural mesothelioma (PM) pathological (p) T staging, patients with fissural invasion are upgraded from T1 to T2. This study aimed to externally validate this staging modification.

Methods: Resected pT1/2 PM patients were selected. The Kaplan-Meier method was applied to assess survival differences, and propensity score matching was utilized to balance baseline characteristics. Univariable and multivariable Cox analyses were conducted to determine prognostic factors. Multiple model parameters were used to evaluate the performance of the ninth and eighth edition pT staging in distinguishing between T1 and T2 patients.

Results: A total of 818 eligible patients were included, among whom 325 initially classified as T1 were reclassified as T2 due to fissural invasion, resulting in 57 patients remaining with pT1 disease. Survival analyses demonstrated that both before and after matching, the ninth edition T staging effectively differentiated between T1 and T2 patients, whereas the eighth edition did not perform as satisfactorily in distinguishing between the groups. Cox regression analyses further confirmed that the ninth edition T staging was a strong prognostic factor, whereas the eighth edition T staging was not prognostic. Lastly, model parameter results indicated that the ninth edition T staging performed better in distinguishing between T1 and T2 patients compared to the eighth edition.

Discussion: Our study provided validation and endorsement for the revisions implemented in the ninth edition pT staging, specifically the reclassification of patients with fissural invasion from pT1 to pT2. This research contributed to the precise staging of PM patients.

Copyright © 2025 Liu, Cai, Li and Weng.

In plain English

This study used the U.S. Surveillance, Epidemiology, and End Results (SEER) cancer database to test a change in post-surgical staging of pleural mesothelioma. The ninth edition of the staging system moves tumors involving the fissure from stage T1 to stage T2. The authors identified 818 patients, diagnosed 2000 to 2021, who had surgery for T1 or T2 pleural mesothelioma. Under the eighth edition, 382 were T1. Under the ninth edition, 325 of these were moved to T2, leaving 57 as T1. Under the ninth edition, T1 patients had a 5-year overall survival rate of 27.5% versus 12.7% for T2 patients (p = 0.008). Under the eighth edition, the difference (15.9% vs. 11.8%) was not statistically significant. In the ninth-edition matched group (49 pairs), after adjusting for other factors, T2 had a hazard ratio for overall survival of 2.019 (confidence interval 1.295 to 3.150) compared with T1. Eighth-edition T stage was not an independent prognostic factor. The authors concluded that their results supported the change. They noted the small number of T1 patients (57), the retrospective design, and missing data on asbestos exposure and type of surgery.

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 analysis of a population cancer registry (SEER), comparing ninth- and eighth-edition pathological T staging
• Who was studied: 818 adult patients with pleural mesothelioma staged T1 or T2 who had surgery and no neoadjuvant therapy. They were selected from 17,746 cases of pleural malignancies diagnosed 2000 to 2021 in the U.S. SEER database.
• Exposure: Asbestos exposure was not studied, because it was not available in the database. The factor examined was fissural invasion, which the ninth edition moves from pathological stage T1 to T2.
• Main results:
  • Under the ninth edition, 57 patients were T1 and 761 were T2. Under the eighth edition, 382 were T1 and 436 were T2. 325 eighth-edition T1 patients were reclassified to T2 because of fissural invasion.
  • Before matching, under the ninth edition, the 5-year overall survival rate was 27.5% for T1 versus 12.7% for T2 (p = 0.008). The 5-year cancer-specific survival rate was 32.3% versus 15.4% (p = 0.012).
  • Before matching, under the eighth edition, there was no significant difference in overall survival between T1 and T2 (5-year rate 15.9% vs. 11.8%, p = 0.133). The 5-year cancer-specific survival rate was 19.4% versus 14.3% (p = 0.174).
  • After propensity score matching in the ninth edition (49 pairs), the 5-year overall survival rate was 27.4% for T1 versus 10.2% for T2 (p less than 0.001). In the eighth-edition matched group (289 pairs), the 5-year overall survival rate was 16.1% versus 10.5% (p = 0.052), and the cancer-specific survival rate was 20.1% versus 12.4% (p = 0.048).
  • In multivariable Cox analysis of the ninth-edition matched cohort, T2 versus T1 had a hazard ratio of 2.019 (1.295 to 3.150, p = 0.002) for overall survival. For cancer-specific survival it was 2.060 (1.298 to 3.260, p = 0.002).
  • In the eighth-edition matched cohort, T stage was not an independent prognostic factor, with a hazard ratio of 1.120 (0.937 to 1.339, p = 0.212) for overall survival.
  • For overall survival, the C-index of the ninth edition (0.514, 0.502 to 0.526) slightly outperformed that of the eighth edition (0.513, 0.492 to 0.534). The AIC was lower for the ninth edition (8,180.463 vs. 8,186.009), and the 5-year NRI+ was 0.396.
• The authors' conclusion: The authors concluded that their study validated and supported the ninth-edition change, particularly moving patients with fissural invasion from pT1 to pT2.
• Limitations the authors state:
  • Maximum pleural thickness was not recorded in SEER, so clinical (cT) staging could not be validated.
  • Only 57 patients were pT1, which could weaken statistical power.
  • Clinical details such as asbestos exposure were unavailable in SEER.
  • The type of surgery (e.g., extrapleural pneumonectomy or pleurectomy/decortication) was not available, so its effect on survival could not be assessed.
  • The retrospective design carries risks of selection bias and unmeasured confounding. For example, surgical patients may have been fitter.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Metastasis, Staging.

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