How Is Mesothelioma Diagnosed? Tests, Biopsies & Specialists

Initial Tests & Imaging

When mesothelioma is suspected, doctors typically begin with imaging tests to identify abnormalities:

• Chest X-ray — Often the first test; may show pleural effusion or thickening
• CT scan (computed tomography) — Provides detailed cross-sectional images; the most commonly used imaging tool for mesothelioma
• PET scan (positron emission tomography) — Helps identify metabolically active cancer cells and detect spread
• MRI (magnetic resonance imaging) — Useful for evaluating tumor extent and involvement of nearby structures
• Echocardiogram — Used when pericardial mesothelioma is suspected

Biopsy: The Gold Standard

Imaging alone cannot definitively diagnose mesothelioma. A biopsy — the removal and laboratory analysis of tissue — is required for a definitive diagnosis. Types of biopsies include:

• Thoracoscopy (VATS) — Video-assisted thoracic surgery to collect pleural tissue; most common and preferred method
• Needle biopsy — A needle is inserted through the chest wall to collect fluid or tissue; less invasive but may yield insufficient tissue
• Laparoscopy — Used for peritoneal mesothelioma; a small camera is inserted into the abdomen
• Open surgery biopsy — Used when other methods are insufficient

Blood Tests & Biomarkers

Several blood biomarkers can support a mesothelioma diagnosis, though none are definitive alone:

• Mesomark (SMRP) — Soluble mesothelin-related peptides; elevated in most pleural mesothelioma patients
• Fibulin-3 — A plasma biomarker that may help distinguish mesothelioma from other conditions
• N-ERC/Mesothelin — Another mesothelin-related biomarker

Finding a Mesothelioma Specialist

Because mesothelioma is rare, it's critical to be treated by specialists with experience in this specific cancer. Look for:

• NCI-designated cancer centers with mesothelioma programs
• Thoracic surgeons who specialize in mesothelioma operations
• Oncologists with mesothelioma-specific research experience
• Pathologists experienced in mesothelioma diagnosis

Major mesothelioma centers include MD Anderson Cancer Center, Memorial Sloan Kettering, Brigham and Women's Hospital, and the University of Chicago.

Why You Need a Second Opinion

Mesothelioma is frequently misdiagnosed — even by experienced oncologists. A second opinion from a mesothelioma specialist can:

• Confirm or correct the diagnosis
• Identify the specific cell type (which affects treatment)
• Open access to clinical trials
• Provide access to more aggressive treatment options

Common Misdiagnoses

Mesothelioma is most commonly misdiagnosed as:

• Lung adenocarcinoma or other lung cancers
• Pleural effusion from other causes
• Pneumonia or pleurisy
• Ovarian cancer (for peritoneal mesothelioma in women)
• Irritable bowel syndrome

The Diagnostic Journey: From Suspicion to Confirmation

Diagnosing mesothelioma is a multi-step process that typically begins when a physician notices an abnormality on imaging studies and ends with pathological confirmation from a tissue biopsy. The process can take weeks to months, during which time patients and families often experience significant anxiety and uncertainty. Understanding each step of the diagnostic process can help patients navigate this challenging period more effectively.

The diagnostic journey typically begins with a primary care physician or emergency room visit prompted by symptoms — most commonly shortness of breath, chest pain, or abdominal distension. A chest X-ray or CT scan is ordered, which may show pleural effusion, pleural thickening, or an abdominal mass. These findings prompt referral to a specialist — typically a pulmonologist for pleural disease or a gastroenterologist for peritoneal disease — who orders additional imaging and ultimately a biopsy.

Imaging Studies in Mesothelioma Diagnosis

CT (computed tomography) scanning is the most important imaging study in mesothelioma diagnosis and staging. CT can show the extent of pleural thickening, the presence and volume of pleural effusion, lymph node involvement, and any spread to adjacent structures. PET (positron emission tomography) scanning is used to identify areas of metabolically active disease and can help distinguish mesothelioma from benign pleural conditions. MRI (magnetic resonance imaging) provides detailed images of soft tissue and is particularly useful for evaluating chest wall invasion and diaphragmatic involvement when surgery is being considered.

While imaging studies are essential for evaluating the extent of disease and planning treatment, they cannot provide a definitive mesothelioma diagnosis. The imaging findings of mesothelioma can be similar to those of other conditions, including metastatic cancer, pleural infections, and benign pleural disease. A tissue biopsy is always required for definitive diagnosis.

Biopsy Techniques

Several biopsy techniques may be used depending on the location and extent of disease. Thoracentesis — draining fluid from the pleural space with a needle — is often the first procedure performed when pleural effusion is present. The fluid can be analyzed for cancer cells, but this method has a diagnostic yield of only about 30% for mesothelioma because cancer cells are not always present in the fluid. CT-guided needle biopsy can sample pleural or peritoneal masses under imaging guidance, with a diagnostic yield of approximately 60-80%.

Video-assisted thoracoscopic surgery (VATS) is the gold standard for diagnosing pleural mesothelioma, with a diagnostic accuracy of over 90%. Under general anesthesia, a small camera and instruments are inserted through small incisions in the chest wall, allowing the surgeon to visualize the pleura directly and take targeted biopsy samples from the most suspicious areas. For peritoneal mesothelioma, laparoscopy — a similar procedure performed in the abdomen — provides the same advantages of direct visualization and targeted sampling.

Pathological Analysis: The Definitive Step

Once a tissue sample is obtained, it is sent to a pathology laboratory for analysis. The pathologist examines the tissue under a microscope and uses a panel of immunohistochemical (IHC) stains to identify the specific proteins expressed by the cells. Mesothelioma cells express certain proteins — including calretinin, WT-1, mesothelin, and D2-40 — that help distinguish them from other cancer types. The combination of positive and negative IHC markers, together with the microscopic appearance of the cells, allows the pathologist to confirm the mesothelioma diagnosis and determine the cell type (epithelioid, sarcomatoid, or biphasic).

Given the complexity of mesothelioma diagnosis and the significant consequences of an incorrect diagnosis, seeking a second pathological opinion from a major cancer center with mesothelioma expertise is strongly recommended. Studies have found that second opinions change the diagnosis or significantly alter the treatment plan in a substantial percentage of mesothelioma cases. Tissue samples and slides can be sent to another institution for review without the patient needing to travel.

Staging: Understanding Disease Extent

After mesothelioma is confirmed, staging tests are performed to determine how far the disease has spread. For pleural mesothelioma, the most widely used staging system is the TNM system, which evaluates the primary tumor (T), lymph node involvement (N), and distant metastases (M). Stage I disease is localized to the pleura on one side. Stage II involves limited spread to the lung or diaphragm. Stage III involves more extensive local spread. Stage IV involves distant metastases or spread to the opposite chest.

Accurate staging is essential for determining whether a patient is a candidate for surgery and for selecting the most appropriate treatment approach. Patients with early-stage disease (Stage I or II) may be candidates for aggressive multimodal therapy, while patients with advanced disease (Stage III or IV) are typically treated with chemotherapy, immunotherapy, or palliative care. Staging also provides important prognostic information and is relevant for legal claims, as more advanced disease generally correlates with higher damages.

Frequently Asked Questions