View source for Mesothelioma Staging

{{#seo:
|title=Mesothelioma Staging: 9th Edition TNM System, Psum Measurement & Stage Groupings
|description=Complete guide to mesothelioma staging systems including the 2025 9th edition TNM with Psum pleural thickness criteria, peritoneal PCI scoring, survival by stage, and treatment algorithms.
|keywords=mesothelioma staging, TNM 9th edition mesothelioma, Psum pleural thickness, mesothelioma stage groupings, peritoneal cancer index PCI, mesothelioma survival by stage, clinical T categories mesothelioma
|image=mesothelioma-staging.jpg
|author=Danziger & De Llano Legal Team
|published_time=2026-03-08
}}
{| class="infobox" style="width:280px; float:right; margin:0 0 1em 1em; border:2px solid #1a5276; border-radius:8px; overflow:hidden;"
|-
! colspan="2" style="background:#1a5276; color:white; padding:12px; font-size:1.1em; text-align:center;" | Mesothelioma Staging
|-
| colspan="2" style="padding:10px; text-align:center; font-style:italic; border-bottom:1px solid #dee2e6;" | TNM 9th Edition (Effective January 1, 2025)
|-
| style="padding:10px; font-weight:bold; width:40%; border-bottom:1px solid #dee2e6;" | Current System
| style="padding:10px; border-bottom:1px solid #dee2e6;" | AJCC/UICC TNM 9th Edition
|-
| style="padding:10px; font-weight:bold; border-bottom:1px solid #dee2e6;" | Key Innovation
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Psum (pleural thickness)
|-
| style="padding:10px; font-weight:bold; border-bottom:1px solid #dee2e6;" | Database
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 3,598 patients, 29 centers
|-
| style="padding:10px; font-weight:bold; border-bottom:1px solid #dee2e6;" | Stage I Median OS
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ~21 months
|-
| style="padding:10px; font-weight:bold; border-bottom:1px solid #dee2e6;" | Stage IV Median OS
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ~12 months
|-
| style="padding:10px; font-weight:bold;" | Peritoneal Staging
| style="padding:10px;" | PCI (0–39)
|-
| colspan="2" style="background:#1a5276; padding:10px; text-align:center;" | <span data-nosnippet class="noai-content">[https://dandell.com/contact-us/ <span style="color:white; font-weight:bold;">Free Case Review →</span>]</span>
|}

= Mesothelioma Staging =

== Overview ==

Mesothelioma staging determines the anatomic extent of disease at diagnosis, guides treatment decisions, and provides a framework for predicting survival.<ref name="nci-treatment" /> The '''9th edition TNM staging system''', published in late 2024 and effective January 1, 2025, represents the most significant revision in mesothelioma staging history.<ref name="gill-t" /> For the first time, '''quantitative tumor size criteria''' — specifically the sum of pleural thickness measurements at three axial CT levels (Psum) — replace the purely qualitative invasion-based approach used since 1994.<ref name="iaslc-database" /> This change was driven by a database of 3,598 patients from 29 centers across 4 continents, with only 36.4% undergoing curative-intent surgery, reflecting the real-world shift toward nonsurgical management.<ref name="iaslc-database" /> Peritoneal mesothelioma uses the '''Peritoneal Cancer Index (PCI)''' as a de facto staging tool, while pericardial and testicular mesothelioma have no formal staging systems due to their extreme rarity.<ref name="mnet-peritoneal" /> Understanding disease stage is critical for patients and families to make informed treatment and legal decisions within applicable filing deadlines.<ref name="dandell-diagnosis" />

'''Mesothelioma staging at a glance:'''
* '''9th edition TNM replaces invasion-based staging with tumor thickness''' — quantitative Psum measurements at three CT levels replace subjective criteria used since 1994
* '''Psum cutpoints define clinical T categories''' — cT1 ≤12 mm, cT2 >12–30 mm, cT3 >30 mm, identified through recursive partitioning of 3,598 patients
* '''Stage I patients survive approximately 21 months''' — with 75% one-year and 33% five-year survival rates
* '''Stage IV drops to approximately 12 months''' — with 52% one-year and just 4% five-year survival
* '''Clinical and pathological T staging differ for the first time''' — because Psum cannot be measured after surgery, clinical staging uses thickness while pathological staging uses invasion
* '''Three previously-used descriptors were eliminated''' — non-transmural diaphragm invasion, lung parenchyma invasion, and endothoracic fascia invasion could not be reliably assessed on CT
* '''Fissural invasion was reclassified from pT1 to pT2''' — validated by an external study of 818 patients showing 17 versus 25.8 months median survival
* '''Peritoneal PCI scores predict surgical outcomes''' — PCI ≤19 is associated with improved survival (p=0.001) across 13 abdominopelvic regions
* '''Only 36.4% of patients in the database had surgery''' — reflecting the real-world shift toward nonsurgical management and making staging applicable to all patients

== Key Facts ==

{| class="wikitable" style="width:100%; margin:0; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:12px; text-align:left;" | Key Facts: Mesothelioma Staging
|-
| style="padding:15px;" |
* '''9th Edition TNM (2025):''' First staging system to incorporate quantitative tumor thickness (Psum) into clinical T categories, replacing subjective invasion-based criteria used since 1994<ref name="gill-t" />
* '''Psum Cutpoints:''' cT1 ≤12 mm; cT2 >12–30 mm; cT3 >30 mm — identified through recursive partitioning analysis across 3,598 patients<ref name="gill-t" /><ref name="iaslc-database" />
* '''Three Descriptors Eliminated:''' 9th edition removed non-transmural diaphragm invasion, lung parenchyma invasion, and endothoracic fascia invasion — none reliably assessed on CT<ref name="gill-t" />
* '''Clinical ≠ Pathological T:''' For the first time in any TNM system, clinical and pathological T staging are not directly linked because Psum cannot be measured after surgery<ref name="wang-validation" />
* '''Fissural Invasion Reclassified:''' Moved from pT1 to pT2, validated by 818-patient external study showing 17 months vs. 25.8 months median survival<ref name="wang-validation" />
* '''Stage I Survival:''' Approximately 75% at 1 year and 33% at 5 years for the earliest-stage disease<ref name="acs-staging" />
* '''Stage IV Survival:''' Approximately 52% at 1 year and 4% at 5 years for metastatic disease<ref name="acs-staging" />
* '''Peritoneal PCI:''' Abdomen divided into 13 regions scored 0–3 each; total 0–39; PCI ≤19 associated with improved survival (p=0.001)<ref name="pci-nature" />
* '''Database Shift:''' Only 36.4% of 9th edition database patients had surgery (down from 64.5% in 7th edition), making staging criteria more applicable to all patients<ref name="iaslc-database" />
* '''N Categories Unchanged:''' 9th edition analysis confirmed 8th edition nodal categories remain prognostically valid — cN0 median 23.2 months vs. cN1 18.5 months<ref name="bille-n" />
|}

== How Has Mesothelioma Staging Evolved? ==

Mesothelioma staging has undergone substantial transformation over five decades, progressing from simple surgical observations to an internationally validated, measurement-based system.<ref name="pass-staging" /><ref name="dandell-malignant" />

=== The Butchart System (1976) ===

The oldest mesothelioma staging system was proposed by Eric Butchart based on a small surgical series, developed before the widespread availability of CT imaging.<ref name="pass-staging" />

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Butchart Stage
! style="background:#1a5276; color:white; padding:10px;" | Definition
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''I'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Tumor confined to the ipsilateral pleura, lung, and pericardium
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''II'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Tumor invading chest wall, mediastinal structures, or thoracic lymph node involvement
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''III'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Tumor penetrating diaphragm to involve peritoneum, or extra-thoracic lymph node involvement
|-
| style="padding:10px;" | '''IV'''
| style="padding:10px;" | Distant hematogenous metastases
|}

Despite its simplicity, the Butchart system remarkably parallels current staging concepts. However, it is no longer used clinically because it was based on a small sample and developed before modern cross-sectional imaging.<ref name="pass-staging" /><ref name="mlc-stages" />

=== The Brigham System (Sugarbaker) ===

Developed by Dr. David Sugarbaker at Brigham and Women's Hospital, this system focused on surgical resectability and lymph node involvement rather than anatomic extent.<ref name="pass-staging" />

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Brigham Stage
! style="background:#1a5276; color:white; padding:10px;" | Definition
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''I'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Resectable tumor, no lymph node involvement
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''II'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Resectable tumor, lymph nodes involved
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''III'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Unresectable — tumor extends into chest wall, heart, diaphragm, or peritoneum
|-
| style="padding:10px;" | '''IV'''
| style="padding:10px;" | Distant metastatic disease
|}

The Brigham system was never widely adopted because its focus on resectability made it relevant only to surgical candidates and departed from standard TNM anatomic staging principles.<ref name="pass-staging" /><ref name="mattorney-stages" />

=== The IMIG/TNM System (1994–Present) ===

In 1994, the International Mesothelioma Interest Group (IMIG) and the IASLC proposed a formal TNM-based staging system, subsequently adopted by the AJCC and UICC.<ref name="pass-staging" /><ref name="gill-t" />

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Edition
! style="background:#1a5276; color:white; padding:10px;" | Era
! style="background:#1a5276; color:white; padding:10px;" | Key Features
! style="background:#1a5276; color:white; padding:10px;" | Surgical %
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 6th/7th
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 1994–2016
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Separate T1a (parietal) and T1b (parietal + visceral); purely invasion-based
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 64.5%
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 8th
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 2018
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Collapsed T1a/T1b into single T1; first exploratory analysis of pleural thickness
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 52.7%
|-
| style="padding:10px;" | '''9th'''
| style="padding:10px;" | '''2025'''
| style="padding:10px;" | '''Psum size criteria for clinical T; three descriptors eliminated; clinical ≠ pathological T'''
| style="padding:10px;" | '''36.4%'''
|}

The progressive decrease in surgical patients across editions — from 64.5% to 36.4% — reflects the real-world shift toward nonsurgical management and makes the 9th edition staging criteria more representative of all mesothelioma patients.<ref name="iaslc-database" /><ref name="mnet-staging" />

== What Are the 9th Edition Clinical T Categories? ==

The landmark change in the 9th edition is the incorporation of '''Psum''' — the sum of maximum pleural thickness measured at three axial CT levels — into clinical T descriptors.<ref name="gill-t" /> This replaces the purely qualitative invasion criteria used since 1994 with objective, reproducible measurements.

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Category
! style="background:#1a5276; color:white; padding:10px;" | Psum Criteria
! style="background:#1a5276; color:white; padding:10px;" | Invasion Criteria
! style="background:#1a5276; color:white; padding:10px;" | Description
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''cT1'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ≤12 mm
| style="padding:10px; border-bottom:1px solid #dee2e6;" | No fissural involvement
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Earliest clinical disease — thin pleural tumor on ipsilateral pleura
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''cT2'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ≤12 mm with local invasion, '''OR''' >12–30 mm regardless
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Fissural involvement, mediastinal fat, or single chest wall focus (if Psum ≤12 mm)
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Moderate disease — thickness-based OR invasion-based qualification
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''cT3'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | >30 mm
| style="padding:10px; border-bottom:1px solid #dee2e6;" | —
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Bulky disease defined purely by thickness measurement
|-
| style="padding:10px;" | '''cT4'''
| style="padding:10px;" | Any
| style="padding:10px;" | Chest wall bone, mediastinal organs, through diaphragm/pericardium, contralateral pleura, pericardial effusion
| style="padding:10px;" | Locally advanced disease with organ invasion
|}

The Psum cutpoints of 12 mm and 30 mm were identified through recursive partitioning analysis and validated across geographic regions and histologic types.<ref name="gill-t" /><ref name="iaslc-database" />

=== Three Eliminated 8th Edition Descriptors ===

The 9th edition removed three qualitative descriptors that cannot be accurately determined on CT imaging:<ref name="gill-t" />

# '''Non-transmural diaphragm invasion''' (formerly cT2) — radiologists cannot reliably distinguish partial from complete diaphragm involvement
# '''Invasion of lung parenchyma''' (formerly cT2) — difficult to differentiate from atelectasis or entrapment on imaging
# '''Endothoracic fascia invasion''' (formerly cT3) — not a discrete anatomic structure identifiable on CT

This simplification acknowledges that prior T descriptors, developed through surgical databases, do not translate reliably to radiologic assessment in an era when most patients never undergo surgery.<ref name="gill-t" /><ref name="dandell-treatment" />

== How Does Pathological T Staging Differ in the 9th Edition? ==

A groundbreaking concept in the 9th edition: clinical and pathological T staging are '''not directly linked'''.<ref name="wang-validation" /> This is unprecedented in TNM staging for any solid cancer.

'''Why they diverge:''' Psum measures pleural thickness on intact CT images, but surgeons typically remove mesothelioma in pieces during extended pleurectomy/decortication, making post-surgical thickness measurement impossible. There is no reproducible pathological counterpart for Psum.<ref name="wang-validation" /><ref name="gill-t" />

=== Key Pathological T Change: Fissural Invasion ===

The single major pathological T revision is the reclassification of '''fissural invasion from pT1 to pT2'''.<ref name="wang-validation" />

An external validation study of 818 patients confirmed this change:<ref name="wang-validation" />
* 325 patients initially classified as pT1 were reclassified to pT2 due to fissural invasion
* Patients with fissural invasion: median survival '''17 months'''
* Patients without fissural invasion: median survival '''25.8 months'''
* Cox regression confirmed 9th edition pT staging was a strong prognostic factor, whereas 8th edition pT staging was not prognostic for distinguishing T1 from T2

{| style="width:100%; border:2px solid #007bff; border-left:5px solid #007bff; border-radius:4px; margin:1em 0;"
|-
| style="padding:15px;" | '''Clinical Significance:''' The separation of clinical and pathological T means that a patient staged as cT1 before surgery may be restaged as pT2 after pathologic examination reveals fissural invasion. Treatment teams must consider both staging tracks when interpreting outcomes and planning adjuvant therapy.<ref name="wang-validation" /><ref name="mlc-treatment" />
|}

== What Are the N and M Categories? ==

=== N Categories (Regional Lymph Nodes) ===

The IASLC analyzed nodal involvement in the 9th edition database and concluded the 8th edition categories remain prognostically valid.<ref name="bille-n" />

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Category
! style="background:#1a5276; color:white; padding:10px;" | Definition
! style="background:#1a5276; color:white; padding:10px;" | Median OS (Clinical)
! style="background:#1a5276; color:white; padding:10px;" | Median OS (Pathological)
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''N0'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | No regional lymph node metastasis
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 23.2 months
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 33.8 months
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''N1'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Metastasis to ipsilateral intrathoracic lymph nodes (bronchopulmonary, hilar, mediastinal)
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 18.5 months
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 25.0 months
|-
| style="padding:10px;" | '''N2'''
| style="padding:10px;" | Metastasis to contralateral intrathoracic or any supraclavicular lymph nodes
| style="padding:10px;" | Shorter
| style="padding:10px;" | Shorter
|}

Resected pN0 patients achieved a 3-year overall survival of 48%. No survival difference was found between single-station and multiple-station nodal metastases.<ref name="bille-n" /><ref name="mnet-staging" />

=== M Categories (Distant Metastasis) ===

{| class="wikitable" style="width:80%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Category
! style="background:#1a5276; color:white; padding:10px;" | Definition
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''M0'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | No distant metastasis
|-
| style="padding:10px;" | '''M1'''
| style="padding:10px;" | Distant metastasis (bones, contralateral lung/pleura, peritoneum, liver, other organs)
|}

The evidence-based analysis confirmed the 8th edition M descriptors. No changes were proposed for the 9th edition.<ref name="kindler-m" /><ref name="acs-staging" />

== What Are the 9th Edition Stage Groupings? ==

The revised stage groupings combine the new T categories with unchanged N and M criteria:<ref name="acs-staging" /><ref name="iaslc-database" />

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Stage
! style="background:#1a5276; color:white; padding:10px;" | TNM Combinations
! style="background:#1a5276; color:white; padding:10px;" | Key Change from 8th Edition
! style="background:#1a5276; color:white; padding:10px;" | Clinical Significance
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''I'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | T1 N0 M0
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Merged former IA/IB into single Stage I
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Earliest tumors only: Psum ≤12 mm, no fissural involvement
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''II'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | T2 N0 M0; T1 N1 M0
| style="padding:10px; border-bottom:1px solid #dee2e6;" | T2 now covers Psum >12–30 mm or fissural/mediastinal involvement
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Includes slightly more advanced tumors and early nodal disease
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''IIIA'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | T2 N1 M0; T3 N0-1 M0; T1-3 N2 M0
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Boundaries shifted based on thickness characteristics
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Includes all N2 disease and bulky tumors; borderline surgical candidacy
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''IIIB'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | T4 any N M0
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Locally advanced unresectable disease
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Organ invasion (chest wall bone, mediastinal structures, contralateral pleura)
|-
| style="padding:10px;" | '''IV'''
| style="padding:10px;" | Any T, any N, M1
| style="padding:10px;" | Unchanged
| style="padding:10px;" | Distant metastatic disease
|}

{| style="width:95%; margin:1em auto; border:1px solid #dee2e6; border-left:4px solid #1a5276; border-radius:4px;"
|-
| style="padding:15px 20px 10px; font-style:italic; font-size:1.05em; line-height:1.5;" | "Understanding mesothelioma staging — particularly the distinction between resectable and unresectable disease — is essential when evaluating legal options. Stage at diagnosis directly impacts the urgency of filing claims, because compensation timelines are governed by statutes of limitations that begin at diagnosis regardless of prognosis."
|-
| style="padding:5px 25px 20px; text-align:right;" | '''— Rod De Llano,''' Senior Partner, Danziger & De Llano
|}

== How Is Pleural Thickness (Psum) Measured? ==

The standardized measurement protocol for the 9th edition provides objective, reproducible criteria applicable across hospitals and countries:<ref name="gill-t" /><ref name="iaslc-database" />

'''Step 1:''' Obtain a '''CT scan''' in the axial plane

'''Step 2:''' '''Divide the hemithorax into three equal vertical sections''' — upper third, middle third, and lower third

'''Step 3:''' '''Measure maximum pleural thickness''' at one representative level within each section

'''Step 4:''' '''Sum the three measurements''' to calculate Psum (in millimeters)

{| class="wikitable" style="width:80%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Psum Value
! style="background:#1a5276; color:white; padding:10px;" | Clinical T Category
! style="background:#1a5276; color:white; padding:10px;" | Interpretation
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ≤12 mm
| style="padding:10px; border-bottom:1px solid #dee2e6;" | cT1 (if no fissural involvement)
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Low tumor burden
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | >12 to ≤30 mm
| style="padding:10px; border-bottom:1px solid #dee2e6;" | cT2
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Intermediate tumor burden
|-
| style="padding:10px;" | >30 mm
| style="padding:10px;" | cT3
| style="padding:10px;" | High tumor burden (bulky disease)
|}

Additionally, '''Fmax''' (maximum thickness at the fissure) greater than 5 mm indicates poor prognosis and contributes to fissural invasion assessment.<ref name="gill-t" />

{| style="width:100%; border:2px solid #28a745; border-left:5px solid #28a745; border-radius:4px; margin:1em 0;"
|-
| style="padding:15px;" | '''Why Psum Matters:''' Previous staging relied entirely on qualitative assessments of invasion (e.g., "does the tumor invade the diaphragm?") that were subjective and inconsistent between radiologists. Psum provides a number that any radiologist at any hospital can measure the same way, dramatically improving staging reproducibility and enabling meaningful comparison across institutions and clinical trials.<ref name="gill-t" /><ref name="iaslc-database" />
|}

== How Is Peritoneal Mesothelioma Staged? ==

Peritoneal mesothelioma has no universally accepted TNM staging system due to insufficient case volumes for validation. The '''Peritoneal Cancer Index (PCI)''' serves as the de facto staging tool, particularly for surgical planning.<ref name="pci-nature" /><ref name="mnet-peritoneal" />

=== How PCI Works ===

* The abdomen is divided into '''13 regions'''
* Each region is scored '''0 to 3''' based on tumor burden: 0 = no visible disease; 1 = tumor ≤0.5 cm; 2 = tumor >0.5–5 cm; 3 = tumor >5 cm or bowel involvement
* '''Total PCI score range: 0–39'''

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | PCI Score
! style="background:#1a5276; color:white; padding:10px;" | Equivalent Stage
! style="background:#1a5276; color:white; padding:10px;" | Surgical Candidacy
! style="background:#1a5276; color:white; padding:10px;" | Prognosis
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''1–10'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Stage 1
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Best candidates for CRS/HIPEC
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Favorable
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''11–20'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Stage 2
| style="padding:10px; border-bottom:1px solid #dee2e6;" | CRS/HIPEC may be beneficial
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Intermediate
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''21–30'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Stage 3
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Marginal surgical candidacy
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Guarded
|-
| style="padding:10px;" | '''31–39'''
| style="padding:10px;" | Stage 4
| style="padding:10px;" | Generally not surgical candidates
| style="padding:10px;" | Poor
|}

PCI ≤19 is associated with improved overall survival (p=0.001), while PCI ≥30 is associated with worse survival (p=0.002).<ref name="pci-nature" /><ref name="mlc-peritoneal" />

=== Pericardial and Testicular Mesothelioma ===

No formal staging systems exist for pericardial or testicular mesothelioma. These exceptionally rare variants (combined less than 5% of all mesothelioma cases) lack sufficient case volumes to develop and validate staging systems. Physicians characterize disease extent descriptively using imaging and surgical findings.<ref name="mattorney-pericardial" /><ref name="dandell-types" />

== What Is the Survival by Stage? ==

=== Pleural Mesothelioma Survival by TNM Stage ===

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Stage
! style="background:#1a5276; color:white; padding:10px;" | 1-Year Survival
! style="background:#1a5276; color:white; padding:10px;" | 2-Year Survival
! style="background:#1a5276; color:white; padding:10px;" | 5-Year Survival
! style="background:#1a5276; color:white; padding:10px;" | Median OS
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''Stage I'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 75%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 41%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 33%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ~21 months
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''Stage II'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 70%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 39%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 9%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ~19 months
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''Stage III'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 62%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 29%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 6%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | ~16 months
|-
| style="padding:10px;" | '''Stage IV'''
| style="padding:10px;" | 52%
| style="padding:10px;" | 24%
| style="padding:10px;" | 4%
| style="padding:10px;" | ~12 months
|}

<small>Source: NCI SEER database; American Cancer Society<ref name="acs-staging" /><ref name="acs-survival" /></small>

=== SEER Summary Stage Survival ===

{| class="wikitable" style="width:80%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | SEER Stage
! style="background:#1a5276; color:white; padding:10px;" | 5-Year Relative Survival
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Localized
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 18%
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Regional
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 11%
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Distant
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 7%
|-
| style="padding:10px;" | All stages combined
| style="padding:10px;" | 12%
|}

<small>Source: NCI SEER database<ref name="acs-survival" /></small>

=== Peritoneal Mesothelioma Survival by Treatment ===

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Treatment
! style="background:#1a5276; color:white; padding:10px;" | 1-Year
! style="background:#1a5276; color:white; padding:10px;" | 3-Year
! style="background:#1a5276; color:white; padding:10px;" | 5-Year
! style="background:#1a5276; color:white; padding:10px;" | Median Survival
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | CRS + HIPEC (CC-0)
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 83%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 62%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 52%
| style="padding:10px; border-bottom:1px solid #dee2e6;" | 33–103 months
|-
| style="padding:10px;" | All peritoneal (SEER)
| style="padding:10px;" | 92%
| style="padding:10px;" | 74%
| style="padding:10px;" | 65%
| style="padding:10px;" | 3–5 years
|}

<small>Source: NCI SEER database; Mesothelioma.net<ref name="mnet-hipec" /><ref name="acs-survival" /></small>

== How Does Stage Determine Treatment? ==

For treatment purposes, mesothelioma staging is often simplified into a binary classification: resectable versus unresectable disease.<ref name="dandell-treatment" /><ref name="mlc-treatment" />

{| class="wikitable" style="width:100%; margin:1em auto; border-collapse:collapse;"
|-
! style="background:#1a5276; color:white; padding:10px;" | Stage
! style="background:#1a5276; color:white; padding:10px;" | Typical Treatment Approach
! style="background:#1a5276; color:white; padding:10px;" | Resectability
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''I–II'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Surgery (P/D or EPP) + adjuvant chemotherapy ± radiation; immunotherapy may be added
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Generally resectable
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''IIIA'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Case-by-case: neoadjuvant chemo/immunotherapy followed by surgery, or definitive chemo-immunotherapy
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Borderline — depends on tumor extent, histology, patient fitness
|-
| style="padding:10px; border-bottom:1px solid #dee2e6;" | '''IIIB'''
| style="padding:10px; border-bottom:1px solid #dee2e6;" | First-line nivolumab + ipilimumab (CheckMate 743 standard); pemetrexed/cisplatin; or clinical trial
| style="padding:10px; border-bottom:1px solid #dee2e6;" | Unresectable
|-
| style="padding:10px;" | '''IV'''
| style="padding:10px;" | Systemic therapy (immunotherapy or chemotherapy); palliative care; clinical trials
| style="padding:10px;" | Unresectable
|}

The 9th edition's improved prognostic discrimination is particularly valuable for clinical trials, enabling more homogeneous treatment arms and consistent enrollment criteria across international sites through standardized Psum measurement.<ref name="gill-t" /><ref name="mnet-treatment" />

{| style="width:100%; border:2px solid #ffc107; border-left:5px solid #ffc107; border-radius:4px; margin:1em 0;"
|-
| style="padding:15px;" | '''Important:''' Mesothelioma staging determines not only treatment options but also the urgency of pursuing legal remedies. Statutes of limitations for mesothelioma lawsuits typically range from 1 to 6 years from diagnosis and run regardless of disease stage or treatment outcome. Even patients with early-stage, resectable disease should promptly consult with experienced mesothelioma attorneys to preserve all legal options.<ref name="dandell-case" /><ref name="mattorney-compensation" />
|}

== Frequently Asked Questions ==

=== What staging system is currently used for mesothelioma? ===

The '''TNM 9th edition''' (AJCC/UICC), effective January 1, 2025, is the current international standard for pleural mesothelioma staging. It is the first version to incorporate quantitative pleural thickness measurements (Psum) into clinical T categories. Peritoneal mesothelioma uses the Peritoneal Cancer Index (PCI), and pericardial/testicular mesothelioma have no formal staging systems.<ref name="gill-t" /><ref name="acs-staging" />

=== What is Psum and why does it matter? ===

Psum is the sum of maximum pleural thickness measured at three axial CT levels (upper, middle, and lower hemithorax). Cutpoints of 12 mm and 30 mm define clinical T categories. Psum matters because it provides an objective, reproducible number that any radiologist at any hospital can measure, replacing the subjective invasion-based criteria that varied between observers.<ref name="gill-t" /><ref name="iaslc-database" />

=== What is the difference between clinical and pathological staging? ===

Clinical staging is based on imaging (primarily CT) and determines the treatment plan before surgery. Pathological staging is based on examination of tissue removed during surgery. In the 9th edition, clinical and pathological T staging are not directly linked — Psum measures thickness on intact CT images, but surgical removal in pieces makes post-surgical thickness measurement impossible.<ref name="wang-validation" /><ref name="gill-t" />

=== Can mesothelioma be diagnosed at an early stage? ===

Early-stage diagnosis is possible but uncommon because mesothelioma symptoms (shortness of breath, chest pain) typically develop only after the disease has progressed. Only about 20% of patients are diagnosed at a localized stage. Early detection through screening of high-risk populations (including those with significant asbestos exposure history) and advances in imaging technology may improve early-stage diagnosis rates.<ref name="acs-staging" /><ref name="dandell-diagnosis" />

=== What is the survival rate for Stage I mesothelioma? ===

Stage I mesothelioma has the best prognosis, with approximately 75% survival at 1 year, 41% at 2 years, and 33% at 5 years. Median overall survival is approximately 21 months. Individual outcomes depend on additional factors including histologic subtype, performance status, age, and treatment approach.<ref name="acs-staging" /><ref name="acs-survival" />

=== How is peritoneal mesothelioma staged? ===

Peritoneal mesothelioma uses the Peritoneal Cancer Index (PCI), which divides the abdomen into 13 regions, each scored 0–3 based on tumor burden (total range 0–39). PCI ≤19 is associated with improved survival. Unlike pleural mesothelioma, there is no formal TNM staging system for peritoneal disease, though a proposal to map PCI to T categories (Yan et al., 2011) exists but has not been widely adopted.<ref name="pci-nature" /><ref name="mnet-peritoneal" />

=== Does staging affect eligibility for clinical trials? ===

Yes. Clinical trials specify stage-based eligibility criteria, and the 9th edition's standardized Psum measurement enables more consistent enrollment criteria across international sites. Better T-category stratification ensures more homogeneous treatment arms. Some trials are restricted to early-stage (resectable) patients, while others focus specifically on advanced-stage (unresectable) disease.<ref name="gill-t" /><ref name="ct-gov" />

=== Why were three staging descriptors removed in the 9th edition? ===

The 9th edition eliminated non-transmural diaphragm invasion, lung parenchyma invasion, and endothoracic fascia invasion from clinical T descriptors because these features cannot be reliably identified on CT imaging. Since most patients now undergo staging with imaging rather than surgery, the criteria needed to reflect what radiologists can actually assess.<ref name="gill-t" />

== Quick Statistics ==

* '''3,598 patients''' from 29 centers across 4 continents formed the database for the 9th edition TNM revision<ref name="iaslc-database" />
* '''36.4%''' of 9th edition database patients underwent curative-intent surgery, down from 64.5% in the 7th edition<ref name="iaslc-database" />
* '''12 mm and 30 mm''' Psum cutpoints define the three clinical T categories (cT1, cT2, cT3) in the 9th edition<ref name="gill-t" />
* '''25.8 vs. 17 months''' median survival for patients without versus with fissural invasion, validating the pT1-to-pT2 reclassification<ref name="wang-validation" />
* '''23.2 vs. 18.5 months''' median overall survival for cN0 versus cN1 disease<ref name="bille-n" />
* '''75% vs. 52%''' one-year survival for Stage I versus Stage IV pleural mesothelioma<ref name="acs-staging" />
* '''33% vs. 4%''' five-year survival for Stage I versus Stage IV disease<ref name="acs-staging" />
* '''18%''' five-year relative survival for localized disease versus 7% for distant disease (SEER summary staging)<ref name="acs-survival" />
* '''PCI ≤19''' associated with improved overall survival in peritoneal mesothelioma (p=0.001)<ref name="pci-nature" />

== Get Help ==

If you or a loved one has been diagnosed with mesothelioma at any stage, understanding staging is a critical step toward making informed treatment and legal decisions. Staging determines both treatment options and the timeline for pursuing compensation.

'''Legal Resources:'''
* [https://dandell.com/ Danziger & De Llano] — Experienced mesothelioma attorneys offering free case evaluations. Call '''(866) 222-9990''' for a confidential consultation.<ref name="dandell-home" />
* [https://mesotheliomalawyersnearme.com/ Mesothelioma Lawyers Near Me] — Find qualified mesothelioma attorneys in your area and access the free case evaluation quiz.
* [https://www.mesotheliomalawyercenter.org/ Mesothelioma Lawyer Center] — Legal resources and attorney matching services for mesothelioma families.<ref name="mlc-home" />

== Related Pages ==

'''Medical Information:'''
* [[Mesothelioma_Diagnosis_and_Staging]] — Comprehensive guide to diagnosis process and staging overview
* [[Mesothelioma_Prognosis]] — Prognostic scoring systems, BAP1 mutations, and survival prediction
* [[Mesothelioma_Survival_Statistics]] — Population-level survival data and treatment outcomes
* [[Understanding_Your_Diagnosis]] — Guide to mesothelioma types and diagnosis
* [[Mesothelioma_Treatment_Centers]] — Specialized cancer centers with mesothelioma programs
* [[Clinical_Trials]] — Current research studies and enrollment opportunities
* [[CheckMate_743_Trial]] — Immunotherapy trial data for unresectable disease

'''Quick Reference:'''
* [[Mesothelioma_Quick_Facts]] — Core statistics and essential data
* [[Veterans_Mesothelioma_Quick_Reference]] — VA benefits and military exposure data

'''Legal Resources:'''
* [[Mesothelioma_Claim_Process]] — Steps from diagnosis to compensation
* [[Statute_of_Limitations_by_State]] — State-by-state filing deadlines
* [[Asbestos_Trust_Funds]] — Trust fund information and filing guidance

== References ==

<references>
<ref name="gill-t">[https://pmc.ncbi.nlm.nih.gov/articles/PMC11380601/ The IASLC Mesothelioma Staging Project: Proposals for Revisions of the T Descriptors in the Forthcoming 9th Edition], ''Journal of Thoracic Oncology'', 2024</ref>
<ref name="iaslc-database">[https://pmc.ncbi.nlm.nih.gov/articles/PMC12063365/ IASLC Pleural Mesothelioma Staging Project: Expanded Database to Inform Revisions in the 9th Edition], ''Journal of Thoracic Oncology'', 2024</ref>
<ref name="wang-validation">[https://pmc.ncbi.nlm.nih.gov/articles/PMC12457411/ External Validation of Pathological T Adjustments in the Ninth Edition Pleural Mesothelioma Staging], ''Frontiers in Oncology'', 2025</ref>
<ref name="bille-n">[https://pubmed.ncbi.nlm.nih.gov/38734073/ The IASLC Mesothelioma Staging Project: Proposals for N Descriptors, 9th Edition], ''Journal of Thoracic Oncology'', 2024</ref>
<ref name="kindler-m">[https://pubmed.ncbi.nlm.nih.gov/39181447/ The IASLC Mesothelioma Staging Project: Proposals for M Descriptors, 9th Edition], ''Journal of Thoracic Oncology'', 2024</ref>
<ref name="pass-staging">[https://pmc.ncbi.nlm.nih.gov/articles/PMC5864645/ Staging in the Era of International Databases], ''Journal of Thoracic Disease'', 2018</ref>
<ref name="pci-nature">[https://doi.org/10.1038/s41598-020-70044-8 Prognostic Role of Radiological PCI in Malignant Peritoneal Mesothelioma], ''Nature Scientific Reports'', 2020</ref>
<ref name="acs-staging">[https://www.cancer.org/cancer/types/malignant-mesothelioma/detection-diagnosis-staging/staging.html Stages of Mesothelioma], American Cancer Society</ref>
<ref name="acs-survival">[https://www.cancer.org/cancer/types/malignant-mesothelioma/detection-diagnosis-staging/survival-statistics.html Survival Rates for Pleural Mesothelioma], American Cancer Society</ref>
<ref name="nci-treatment">[https://www.cancer.gov/types/mesothelioma/patient/mesothelioma-treatment-pdq Mesothelioma Treatment (PDQ) — Patient Version], National Cancer Institute</ref>
<ref name="ct-gov">[https://clinicaltrials.gov/search?cond=Mesothelioma Mesothelioma Clinical Trials], ClinicalTrials.gov</ref>
<ref name="dandell-diagnosis">[https://dandell.com/mesothelioma-diagnosis/ Mesothelioma Diagnosis Guide], Danziger & De Llano</ref>
<ref name="dandell-malignant">[https://dandell.com/malignant-mesothelioma/ Malignant Mesothelioma], Danziger & De Llano</ref>
<ref name="dandell-treatment">[https://dandell.com/mesothelioma/mesothelioma-diagnosis/pleural-vs-peritoneal-mesothelioma-differences/ Pleural vs Peritoneal Mesothelioma Differences], Danziger & De Llano</ref>
<ref name="dandell-types">[https://dandell.com/mesothelioma/types/ Types of Mesothelioma], Danziger & De Llano</ref>
<ref name="dandell-case">[https://dandell.com/whats-your-case-worth/ What's Your Mesothelioma Case Worth?], Danziger & De Llano</ref>
<ref name="dandell-home">[https://dandell.com/ Asbestos & Mesothelioma Lawyers], Danziger & De Llano</ref>
<ref name="mlc-stages">[https://www.mesotheliomalawyercenter.org/mesothelioma-cancer/stages/ Stages of Mesothelioma], Mesothelioma Lawyer Center</ref>
<ref name="mlc-treatment">[https://www.mesotheliomalawyercenter.org/mesothelioma-cancer/treatment/ Mesothelioma Treatment Guide], Mesothelioma Lawyer Center</ref>
<ref name="mlc-peritoneal">[https://www.mesotheliomalawyercenter.org/peritoneal-mesothelioma-cancer/ Peritoneal Mesothelioma Cancer], Mesothelioma Lawyer Center</ref>
<ref name="mlc-home">[https://www.mesotheliomalawyercenter.org/ Find Top Mesothelioma Attorneys], Mesothelioma Lawyer Center</ref>
<ref name="mnet-staging">[https://mesothelioma.net/mesothelioma-staging/ Staging System for Pleural Mesothelioma Revised], Mesothelioma.net</ref>
<ref name="mnet-peritoneal">[https://mesothelioma.net/peritoneal-mesothelioma/ Peritoneal Mesothelioma], Mesothelioma.net</ref>
<ref name="mnet-hipec">[https://mesothelioma.net/heated-intraperitoneal-chemotherapy/ Heated Intraperitoneal Chemotherapy (HIPEC)], Mesothelioma.net</ref>
<ref name="mnet-treatment">[https://mesothelioma.net/treatment-for-mesothelioma/ Mesothelioma Treatment], Mesothelioma.net</ref>
<ref name="mattorney-stages">[https://mesotheliomaattorney.com/mesothelioma/stages/ Mesothelioma Stages], MesotheliomaAttorney.com</ref>
<ref name="mattorney-pericardial">[https://mesotheliomaattorney.com/mesothelioma/types/pericardial/ Pericardial Mesothelioma], MesotheliomaAttorney.com</ref>
<ref name="mattorney-compensation">[https://mesotheliomaattorney.com/mesothelioma/compensation/ Mesothelioma Compensation Guide], MesotheliomaAttorney.com</ref>
</references>

[[Category:Mesothelioma]]
[[Category:Staging]]
[[Category:Medical Information]]
[[Category:Diagnosis]]
[[Category:TNM Classification]]
[[Category:Peritoneal Mesothelioma]]
[[Category:Treatment]]