Diagnosis and staging
Mesothelioma can look like other diseases on a scan. In most cases, the only way to know for sure is to look at a tissue sample under a microscope.
Last reviewed October 27, 2026 against the sources listed at the end of this page.
In short
- Imaging (x-ray, CT, MRI, PET) finds suspicious areas and shows how far they reach.
- Draining fluid can relieve symptoms, but fluid alone often cannot confirm mesothelioma.
- A biopsy, often by thoracoscopy (VATS) or laparoscopy, is usually needed to confirm it and to name the cell type.
- Only pleural mesothelioma has a formal staging system (AJCC stages I to IV).
- Ask for a copy of your pathology report. You will need it for medical second opinions and for any claim.
Step 1: history and exam
The American Cancer Society says a doctor will start with your symptoms and risk factors, especially asbestos exposure. Fluid around the lungs (pleural effusion), in the abdomen (ascites), or around the heart (pericardial effusion) may be noticed during a physical exam.
Step 2: imaging tests
| Test | What it is | What it can show |
|---|---|---|
| Chest x-ray | A quick picture of the chest | Thickening or calcium deposits on the pleura, fluid, changes from asbestos |
| CT scan | Detailed cross-section x-rays | The size and location of thickening or tumors, and spread |
| MRI | Pictures made with magnets and radio waves | Soft-tissue detail, such as whether a tumor has grown into the diaphragm or chest wall |
| PET or PET/CT scan | A scan using a small amount of radioactive sugar | Areas of active cancer and possible spread |
| Echocardiogram | An ultrasound of the heart | Fluid around the heart and how well the heart pumps |
Step 3: fluid and blood tests
If fluid has built up, a doctor can remove some with a needle. The procedure has a different name in each place: thoracentesis (chest), paracentesis (abdomen), and pericardiocentesis (around the heart). The American Cancer Society cautions that even when no cancer cells are found in the fluid, a person may still have cancer.
Blood tests for markers such as soluble mesothelin-related peptides can support a diagnosis, but they are not enough on their own.
Step 4: biopsy
A biopsy takes a small sample of tissue for the lab. Common methods include:
- Needle biopsy, guided by a CT scan or ultrasound. It is less invasive, but the sample may be too small to tell the cell type.
- Thoracoscopy (also called VATS): a small camera placed through a cut in the chest to look at the pleura and take samples. It is done under general anesthesia.
- Laparoscopy: the same idea for the abdomen.
- Surgical biopsy, when a larger sample is needed.
The pathologist examines the sample, often with extra lab tests, to tell mesothelioma apart from other cancers and to name the subtype: epithelioid, sarcomatoid, or biphasic. A second review of the slides at a center that sees many mesothelioma cases is common and reasonable to request.
Step 5: staging
The stage describes how far the cancer has spread. The American Cancer Society explains that pleural mesothelioma is the only type with a formal staging system, the American Joint Committee on Cancer (AJCC) TNM system:
- T describes the main tumor and how far it has grown into nearby tissue.
- N describes spread to lymph nodes.
- M describes spread to distant parts of the body.
These combine into stages I through IV. Doctors also describe a tumor as resectable (it can be removed with surgery) or unresectable. Peritoneal and pericardial mesothelioma have no formal system, but doctors still map the spread to plan treatment.
A clinical stage comes from exams and scans. A pathological stage comes from surgery and is often more accurate.
Keep your records
Ask for copies of the pathology report, imaging reports, and the doctor's notes that state the diagnosis. You will want them for second opinions, VA claims, trust fund claims, and any lawsuit. Never send these documents through a website form; a lawyer or claims representative will tell you how to share them securely.
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Start the free reviewThis page is general health information, summarized from the sources below. It is not medical advice. Talk with your own doctor or care team about your situation.