Stages of Mesothelioma

Understanding Mesothelioma Staging

Staging describes how far mesothelioma has spread from its point of origin. When doctors diagnose mesothelioma, one of the first and most important steps is determining the stage of the disease. The stage directly shapes the treatment plan, helps predict prognosis, and determines eligibility for surgery and clinical trials. For patients and their families, understanding the staging system is essential for making informed medical and legal decisions.

The TNM Staging System (AJCC 8th Edition)

The standard staging system for malignant pleural mesothelioma is the TNM system, maintained by the American Joint Committee on Cancer (AJCC). The current version, the 8th edition (published 2017), classifies mesothelioma based on three factors:

• T (Tumor) — the size and extent of the primary tumor, including which layers of the pleura and nearby structures are involved
• N (Nodes) — whether cancer has spread to regional lymph nodes, and if so, which lymph node stations are affected
• M (Metastasis) — whether cancer has spread to distant sites in the body, such as the opposite lung, liver, bones, or brain

Doctors use a combination of imaging studies (CT scans, PET scans, MRI) and surgical biopsies to assign T, N, and M values. These values are then combined to determine the overall stage, from Stage 1 (most localized) through Stage 4 (most advanced). It is important to note that only malignant pleural mesothelioma has a formal TNM staging system. Peritoneal mesothelioma, pericardial mesothelioma, and testicular mesothelioma do not have standardized staging systems and are evaluated using different clinical criteria.

Other Staging Systems

While the TNM system is the current clinical standard, two older staging systems are still occasionally referenced in medical literature:

• Butchart System — the oldest staging system for mesothelioma, developed in 1976 by Dr. Eric Butchart. It classifies mesothelioma based solely on the extent of the primary tumor mass and is less precise than the TNM system. It does not account for lymph node involvement as a separate factor.
• Brigham System — developed at Brigham and Women's Hospital by Dr. David Sugarbaker, this system stages mesothelioma based on surgical resectability and lymph node status. It was designed to help determine which patients were candidates for aggressive surgery.

Stage 2 Mesothelioma

In Stage 2 mesothelioma, the tumor has grown beyond the pleural lining and may have begun to invade nearby structures such as the diaphragm, lung tissue, or the chest wall. However, the cancer remains on one side of the body and has not spread to lymph nodes or distant organs in most Stage 2 classifications. Many Stage 2 patients are still considered candidates for surgery, though the extent of surgical resection may be more limited than in Stage 1.

TNM Classification

• Stage 2 (T1-T2 N1 M0 or T3 N0 M0) — the tumor may involve both pleural layers and adjacent structures, or there may be limited ipsilateral (same-side) lymph node involvement. The cancer has not metastasized to distant sites.

Treatment Options

Stage 2 patients may still be candidates for curative-intent surgery, depending on the extent of tumor involvement and the patient's overall health. The same surgical options available to Stage 1 patients (P/D and EPP) may be considered, though the decision depends on how deeply the tumor has invaded surrounding tissue.

Multimodal treatment — combining surgery with chemotherapy and potentially radiation — remains the standard approach. Neoadjuvant chemotherapy (given before surgery to shrink the tumor) may be recommended for some Stage 2 patients to improve surgical outcomes. Immunotherapy combinations, particularly nivolumab plus ipilimumab, are also increasingly used based on the results of the CheckMate 743 trial.

Stage 4 Mesothelioma

Stage 4 is the most advanced stage of mesothelioma. At this point, the cancer has metastasized — spread to distant sites beyond the original pleural cavity. Common sites of distant metastasis include the opposite lung, the liver, bones, the peritoneum (abdominal lining), and the brain. Treatment at Stage 4 focuses on palliative care: managing symptoms, maintaining quality of life, and extending survival as long as possible.

TNM Classification

• Stage 4 (Any T, Any N, M1) — distant metastasis is present regardless of the size of the primary tumor or the extent of lymph node involvement. Once mesothelioma has spread to distant organs, it is classified as Stage 4.

Treatment Options

Curative surgery is generally not an option at Stage 4. Treatment focuses on systemic therapies and palliative procedures to manage symptoms:

• Chemotherapy — pemetrexed-based regimens remain the first-line systemic treatment, aimed at slowing tumor growth and extending survival
• Immunotherapy — nivolumab plus ipilimumab (approved by the FDA in 2020 for unresectable mesothelioma) has shown improved survival in advanced-stage patients compared to chemotherapy alone
• Palliative procedures — thoracentesis (draining fluid from the chest), pleurodesis (sealing the pleural space to prevent fluid buildup), and pain management to maintain comfort and breathing capacity
• Clinical trials — patients with advanced mesothelioma may qualify for clinical trials testing new immunotherapy agents, gene therapies, and targeted treatments

How Staging Affects Treatment Decisions

The stage of mesothelioma is the primary factor physicians use to determine which treatments are appropriate. Staging guides virtually every clinical decision, from whether surgery is feasible to which drug combinations are recommended.

Surgical Candidacy

Surgery offers the best chance of extending survival for mesothelioma patients, but not all patients are candidates. Staging determines surgical eligibility:

• Stage 1 and Stage 2 patients are generally considered candidates for curative-intent surgery, provided they are otherwise healthy enough to tolerate the procedure. Early-stage diagnosis significantly expands treatment options.
• Stage 3 patients may qualify for limited cytoreductive surgery, but the goal shifts from cure to tumor burden reduction. The decision depends on the specific sub-stage, location of lymph node involvement, and the patient's performance status.
• Stage 4 patients are generally not surgical candidates for curative procedures. Palliative surgical procedures (such as thoracentesis or pleurodesis) may be performed to manage symptoms.

Clinical Trial Eligibility

Many clinical trials for mesothelioma have specific staging requirements. Some trials enroll only early-stage patients to test neoadjuvant therapies, while others are designed specifically for advanced-stage patients who have exhausted standard treatments. Accurate staging is essential for identifying which trials a patient may be eligible to participate in. Your oncologist or a mesothelioma specialist can help match your stage and diagnosis profile with currently enrolling trials.