How Mesothelioma Is Diagnosed

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Mesothelioma represents a serious cancer associated with prior asbestos exposure. If you have symptoms such as trouble catching your breath, coughing, or a wheeze that will not go away, you may be dealing with a very common complication of lung disease—pleural effusion, or fluid around the lung. When you come to your healthcare provider with these symptoms, they will want to perform some tests to better understand what is causing them. Imaging such as CT scans, ultrasound, or MRI is often used to initially identify physical signs of cancer like lesions and masses, or to identify other possible causes. Depending on the outcome, a healthcare provider may proceed to taking a tissue sample, or biopsy, to better understand the nature of the problem and to apply the most effective treatment.

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Mesothelioma cannot be effectively distinguished from other causes of related pulmonary (lung) symptoms based on self-assessment that you may do at home. It is important to see a healthcare provider if you have common mesothelioma symptoms, including a persistent cough, chest pain, fatigue, weakness, and others.

Physical Examination

People with mesothelioma, lung disease, or other forms of cancer often have similar symptoms present. Initially, a healthcare provider will likely ask questions about what exacerbates symptoms (makes them worse), then perform diagnostic tests to better understand these symptoms, including a physical examination, blood tests, and imaging. In particular, imaging gives healthcare providers a better idea of what is causing symptoms and also may reveal possible cancerous cells.

Labs and Tests

Blood and urine tests are likely to be performed to rule out infection or inflammation, assess your general health, and for further diagnostic testing.

If initial imaging reveals a characteristic pleural effusion, masses, or lesions, your healthcare provider will likely want to arrange a biopsy. A biopsy involves removing tissue or fluid from inside the lung or the surrounding chest cavity.

Some people may have medical restrictions that increase the complications of biopsy, making it inadvisable. Others might have a clear history suggesting a high likelihood of mesothelioma, like heavy exposure to asbestos, so less testing is needed. Everyone’s situation is different, and it can be unnerving to have to worry about undergoing a surgical procedure, but biopsy is a very effective method of finding the cause of symptoms and potentially treating mesothelioma. 

Below is a non-exhaustive list of possible procedures. Several have variations. Always follow your healthcare provider's instructions before undergoing a test. Common instructions are to avoid eating and drinking eight hours prior to the biopsy and avoid blood thinners, though exact restrictions vary depending on the type of biopsy being performed and whether you will be sedated.


Thoracentesis is the least invasive diagnostic tool in this category but also not entirely conclusive as a diagnostic tool. Thoracentesis is when fluid is removed from the space between the lungs and the chest wall using a needle inserted between the ribs. A pulmonologist applies a local numbing agent into the chest, then a fine needle is inserted between the ribs under guidance by one of the previously mentioned imaging techniques. 

During insertion, or while the fluids are being removed, there can be feelings of discomfort, pain, or the need to cough, but it is important to stay still while the healthcare provider performs the thoracentesis to avoid increasing the risk of injury to the lung. Once fluid that has built up between the chest wall and lung has been removed there may be some relief of breathing problems. The fluid removed can then be sent and tested in the lab, but results are not always conclusive as far as cancer type. Further biopsy procedures may be required.

CT-Guided Needle Biopsy

A CT-guided needle biopsy is the most straightforward of the biopsies. Under general anesthetic, and sometimes sedation, a needle is inserted to remove a tissue sample from a lesion or mass, guided by a CT scan. The sample is used to determine whether the lesion is cancerous and what kind of cancer it is.

This CT-guided procedure has some possible complications such as deflation of the lung (pneumothorax), bleeding, and infection, but these complications are usually minor. Risks that occur may be common to all surgical procedures. A successful CT-guided needle biopsy has the benefit of a quick recovery time, with most people being able to leave the site of the procedure the day it occurs. It is also less invasive than other surgical biopsy methods.

The other forms of biopsy are surgical and may involve sedation in an operating room.

Thoracoscopy-Guided Biopsy

Thoracoscopy-guided biopsy is a technique where an endoscope is inserted into the back of the torso through small incisions and a camera feed is used to visually confirm lesions along the lung that had previously been spotted with imaging. Pleural lesions are then removed for study. Thoracoscopy can be extremely effective in finding and diagnosing tumors, and can also be used to medically seal lesions (pleurodesis) that are causing fluid to fill the lung.

Open Thoracotomy

The more invasive open thoracotomy is usually only necessary if other methods cannot obtain enough sample tissue for testing. Open thoracotomy is when the chest is opened to visually find and remove lesions for testing.


When fluid material or tissue are removed through a biopsy, they can be tested with immunohistochemistry (IHC) for specific biomarkers present on the surface of the tumors cells. Compared to lung cancer, for example, mesothelioma has its own set of biomarkers, and analyzing various biomarkers can help differentiate between the two conditions.


The initial physical examination is usually followed by X-ray or CT imaging which will help medical professionals locate tumors and identify issues affecting the lungs such as pleural effusion. A pleural effusion, characterized by fluid build-up around the lungs, causes trouble breathing and chest pain. It is a non-specific finding, however; it may be caused by any number of diseases.

X-ray radiography is used to image any unusual structures in and around the lungs. A chest X-ray is one of the the first tests done to evaluate the lungs and the pleura. A Chest X-ray may detect the presence of a pleural effusion and can be used for screening purposes.

Computed tomography (CT) scans combine X-ray images. This is more sensitive and specific than individual X-ray images for the diagnosis of mesothelioma, but it cannot be used to discern whether cancer cells have originated in the mesothelium of the lungs or metastasized to this location from elsewhere.

Ultrasound can also be used to detect or monitor the location and size of a pleural effusion. A gel is applied to the sides of the chest under the arm by a sonographer (someone who performs ultrasounds) which helps conduct sound waves for imaging. Pressing the transducer tool against the skin, sonographers can view fluid present around the lung. They may move the transducer up toward the chest to view other parts of the lung. Ultrasound is sensitive in detecting smaller amounts of fluid, so it can identify a more minor pleural effusion than that which would be detected via X-ray imaging.

Intraoperative ultrasound (that is, an ultrasound performed during surgery) can also be used to find lesions of the lung and pleura while taking a tissue biopsy. 

Fluorodeoxyglucose-Positron emission tomography (FDG PET) scans is an imaging test that uses an intravenous derivative of radioactive glucose (FDG) in order to assess the metabolism of different tissues. Many cancers have an increased metabolism and will light up on a PET scan. A CT scan is usually done in combination with an FDG-PET scan in order to better localize the tumor and to better evaluation of its size.

However, PET scans can give false negatives for less aggressive cancers and false positives for other types of inflammation caused by disease unrelated to cancer. PET scans, and other imaging studies, are not entirely able to determine whether cancer cells have originated in the pleura (lung mesothelium) or metastasized from elsewhere.

Status Update Imaging

During treatment, your healthcare provider will want to monitor the response to treatment. After treatment completion follow up will also be needed to rule out recurrent disease. The monitoring during and after treatment of mesothelioma is most commonly done with chest CT scans. .

Differential Diagnoses

Other malignant conditions (sarcomas, lung cancers, metastatic cancers) can look similar both clinically and radiographically to mesothelioma and may even look similar under the microscope. IHC patterns of staining can help distinguish between other types of cancer and mesothelioma. Also, pleural effusions may also be associated with other benign medical conditions. Testing may help to distinguish these different causes, but consider the following potential diagnoses that may be similar to mesothelioma:

If one procedure is inconclusive in determining the cause, and it is necessary to prepare for another, it is understandably frustrating. Nobody wants to be poked with needles. But getting helpful results in a timely manner is not just good for your treatment and health—it’s good for your state of mind, too. 

A Word From Verywell

It is scary to contemplate the possibility of having a serious medical condition like mesothelioma. If you have been exposed to asbestos, the thought of pursuing a diagnosis may be something you'd rather avoid. Rather than denying the possibility, seek out the appropriate evaluation with testing. In some cases, early detection may afford the opportunity for treatment that may not otherwise be possible. If you experience symptoms concerning for mesothelioma, seek out the diagnostic testing needed to give yourself the best chance to pursue effective treatment.

1 Source
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  1. Frank E. Mott. Mesothelioma: A review. The Ochsner Journal. 2012;(12): 70–79.

Additional Reading

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.