Mesothelioma: Diagnosis

Approved by the Cancer.Net Editorial Board, 05/2016

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. To see other pages, use the menu.

Doctors use many tests to find, or diagnose, cancer. They also do tests to learn if cancer has spread to another part of the body from where it started. If this happens, it is called metastasis. For example, imaging tests can show if the cancer has spread. Imaging tests show pictures of the inside of the body. Doctors may also do tests to learn which treatments could work best.

For most types of cancer, a biopsy is the only sure way for the doctor to know whether an area of the body has cancer. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis.

This list describes options for diagnosing this type of cancer, and not all tests listed will be used for every person. Your doctor may consider these factors when choosing a diagnostic test:

  • The type of cancer suspected

  • Your signs and symptoms

  • Your age and medical condition

  • The results of earlier medical tests

The diagnosis of mesothelioma is challenging, and it can be confused with other diseases, such as lung cancer.

Many people first notice symptoms of mesothelioma when they develop fluid in the space around the lungs, a condition called pleural effusion, or in the abdomen, called ascites. When this fluid is removed, it can be analyzed to find out if there are cancer cells in it. However, testing this fluid is usually not the only test needed to diagnose the disease. A biopsy is usually needed to diagnose mesothelioma.

  • Biopsy. A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis. A pathologist then analyzes the sample(s). A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease. A biopsy is usually needed to confirm a diagnosis of mesothelioma. Sometimes, a needle can be used to get a sample of the lining. More often the doctor removes a tissue sample by using a thin, lighted tube inserted through a small incision in the body. This is called a video thoracoscopy when used to get samples from inside the chest or a laparoscopy when used to get tissue samples from inside the abdomen.

The following procedures may be used to help develop a treatment plan:

  • Physical examination. A physical examination may include:

    • A look at the person’s medical history and his or her family's past illnesses

    • Possible risk factors, including asbestos exposure

    • An examination for other signs of cancer

  • Lung function tests. Also called pulmonary function tests or PFTs, lung function tests evaluate how much air the lungs can hold, how quickly air can move in and out of the lungs, and how well the lungs add oxygen and remove carbon dioxide from the blood.

  • X-ray. An x-ray is a way to create a picture of the structures inside of the body using a small amount of radiation. It is not the main way to diagnose mesothelioma. But, a chest x-ray can sometimes help doctors determine whether a person has mesothelioma and where it is located.

  • Computed tomography (CT or CAT) scan. A CT scan creates a 3-dimensional picture of the inside of the body using x-rays taken from different angles. A computer then puts these images into a detailed, cross-sectional view that shows abnormalities or tumors. A CT scan can also be used to measure the tumor’s size. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein or given as a pill to swallow.  

  • Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRI can also be used to measure the tumor’s size. A special dye called a contrast medium is given before the scan to create a clearer picture. This dye can be injected into a patient’s vein or given as a pill to swallow.

  • Positron emission tomography (PET) or PET-CT scan. A PET scan is usually combined with a CT scan (see above), called a PET-CT scan. However, you may hear your doctor refer to this procedure just as a PET scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radiolabeled sugar substance is injected into the patient’s body. This sugar substance is taken up by cells that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radiolabeled  substance. A scanner then detects this substance to produce images of the inside of the body.

After diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is cancer, these results also help the doctor describe the cancer; this is called staging.

The next section in this guide is Stages. It explains the system doctors use to describe the extent of the disease. Or, use the menu to choose another section to continue reading this guide.