To diagnose mesothelioma, doctors conduct a thorough physical exam followed by specific tests designed to distinguish mesothelioma from all the other types of cancer. Imaging tests, blood tests, and biopsies are the main tools used to confirm a diagnosis.
Imaging tests take “pictures” of the inside of a patient’s body. This is an effective way for doctors to find potentially cancerous areas, and to see where and how the cancer may have spread. There are different types of imaging tests, which include:
Chest X-ray: This is typically the first test doctors use to explore the underlying causes of a bad cough or shortness of breath. An X-ray creates a two-dimensional image, and can reveal abnormal thickening, fluid, or calcium deposits, any of which could indicate mesothelioma. This test takes approximately 30 minutes, which includes the time needed to process the X-ray films and repeat any images, if necessary.
CT scans (computerized tomography scans): A CT scan is more involved than an X-ray. During this test the patient lies still on a narrow table while a scanner rotates around him, taking multiple pictures. A computer combines these pictures to create one detailed image of the soft tissues inside the body. This test can pinpoint the exact location and help determine the stage of the cancer. Mesothelioma diagnoses are ranked in stages from 1 to 4 depending on how much the cancer has spread within the body. A stage 4 mesothelioma is the most advanced diagnosis. This test takes less than 1 hour.
Echocardiogram: This test is likely to be ordered if a doctor suspects the presence of fluid around a patient’s heart, which may indicate pericardial mesothelioma. The test will also reveal how effectively the patient’s heart is pumping. This test can take anywhere from 15 minutes to 1 hour.
PET scan (positron emission tomography scan): For this test, patients are injected with a small amount of radioactive material. While this may sound alarming, the amount of radioactivity used is very low. Any existing cancer cells will absorb the radioactive material more quickly than healthy cells will—and this reaction highlights the area where the cancer is located. This test takes about 30 minutes, and is useful in both finding and staging the cancer.
MRI scan (magnetic resonance imaging scan): These scans provide detailed images of the body’s soft tissue and can reveal the precise location and size of a tumor. Because MRIs identify the amount of damage surrounding a cancerous area, the test is useful in deciding whether surgery is an option. This test can take up to 1 hour.
Mesothelioma can alter the makeup of a person’s blood. High levels of the protein osteopontin and certain peptides—which are amino acids that essentially act as protein building blocks—are often indicators that mesothelioma is present in a patient’s body. While blood tests are not specifically used to diagnose mesothelioma, they add to a doctor’s understanding of the extent of a patient’s disease, and can help predict the long-term outlook. Blood tests take just a few minutes.
New blood tests that identify elevated levels of certain substances in mesothelioma patients might one day become useful tools for earlier diagnosis and for monitoring the progression of mesothelioma. This is hopeful news, as early diagnosis opens the door for more treatment options.
A biopsy is a sample of the fluid or tissue either in or surrounding a tumor. The sample can be removed surgically or with a long, hollow biopsy needle. All samples are sent to a pathology lab, where the cells are examined under a microscope and tested for the presence of cancer cells. This visual proof of the presence of cancer cells is the only definite way doctors can confirm mesothelioma. Even then, the diagnosis can be tricky, as mesothelioma cancer cells can look a lot like other types of cancer cells. For example, pleural mesothelioma is similar to lung cancer, and peritoneal mesothelioma in women resembles some cancers of the ovaries. This test can take anywhere from just a few minutes for a needle biopsy to several hours and potentially an overnight stay in the hospital for a surgical biopsy.
To be absolutely certain of the diagnosis, doctors often order specialized lab tests to help distinguish mesothelioma from other cancers. Those tests can include:
- Immunohistochemistry, which helps distinguish mesothelioma from lung cancer.
- DNA microarray analysis, which looks at patterns of genes in the cells. Mesothelioma cells have different gene patterns from other cancer cells.
- Electron microscopy, which uses a more powerful microscope to magnify fluid and tissue samples, making the smallest parts of cancer cells visible.
Once a diagnosis of mesothelioma is confirmed, doctors may recommend additional tests to determine the stage of the cancer before discussing a treatment plan.