How is mesothelioma diagnosed?

Mesothelioma is usually diagnosed after a person goes to a doctor because they are experiencing symptoms. These symptoms depend on the type of mesothelioma and may include shortness of breath, pain in chest, and fluid retention for pleural mesothelioma, or abdominal pain, fatigue and ascites in the case of peritoneal mesothelioma.

Methods for diagnosing mesothelioma cancer may involve:

Once diagnosed, doctors use a staging system to determine the stage of mesothelioma.

Medical history and exam

One of the first things your doctor may do is to perform a history and physical. The history involves learning about when the symptoms started and any mesothelioma risk factors you might have such as exposure to asbestos. It may also include your medical history, any drugs you are currently taking, your family’s health history (because some conditions have a genetic component), and any other information you wish to share.

A physical is exactly that. The doctor will examine you. The first part of any examination is observation. The doctor will look at you by taking into consideration skin, gait, handshake, muscle tone, posture, etc. Then the doctor may use their stethoscope, and palpate (examine by touch) certain parts of your body or use other medical equipment for a closer look. Since pleural mesothelioma can cause fluid to build up around the lungs (called pleural effusion) the doctor may look for these signs. In peritoneal mesothelioma, fluid can build up in the abdomen (called ascites) and the doctor’s examination may focus on that. If your licensed healthcare provider thinks that mesothelioma is a possibility, further tests will be ordered. These may include imaging tests, removing fluid for testing, a biopsy, and other procedures.

Imaging tests

Imaging tests are used to look inside a patient’s body. Examples of the tests used in mesothelioma include X-rays, CT scans, MRI’s, and PET scans. These tests may be performed to help with diagnosis, check if there is metastasis (in the case of cancer), and even to see if a particular treatment is working and whether the cancer has become temporarily smaller. (Doctor’s call that a “response.”)

Removing fluid for testing

Mesothelioma is cancer of the mesothelial tissue. This tissue, when healthy, produces a lubricating fluid. This fluid allows the lung cavity to expand and contract smoothly with each breath. It performs a similar function in the abdomen. When this mesothelial tissue turns cancerous as it does in mesothelioma, the cells produce too much fluid. The fluid accumulates becoming pleural effusion in the case of pleural mesothelioma or ascites in the case of peritoneal mesothelioma. Clinicians may test this fluid to detect cancer cells. If cancer cells are detected, doctors may then employ the “gold standard” – a tissue biopsy.

Tissue biopsy

A tissue biopsy simply means that the clinician removes a part of the suspected tissue (suspected mesothelioma) for closer examination. Most biopsies are done with a needle and may use a CT scan to help the doctor guide the needle into the correct tissue to take a sample.
Read more about biopsies here.

Pathology diagnosis

Regardless of the manner in which they are obtained, all biopsy and fluid samples are sent to a pathologist. Pathologists use microscopes and special stains and assays to find out if the samples contain mesothelioma. If mesothelioma is diagnosed by the pathologist, the doctor may also determine the mesothelioma cell type. Most mesotheliomas are classified as either epithelioid, sarcomatoid, or mixed/biphasic. Epithelioid generally has the best prognosis.

Pulmonary function tests for Pleural Mesothelioma

If pleural mesothelioma has been diagnosed, a pulmonary function test may be performed to see how well your lungs are working. This test can give the surgeon a better idea if surgery may be a treatment option.

This summarizes some of the tests used to help doctors diagnose mesothelioma. However, these procedures are improving and evolving all the time and your doctor may be using an approach not described here.

Zebras and the Challenge of Diagnosing Mesothelioma

Mesothelioma symptoms, especially the initial ones, can indicate many things. Therefore, many patients are misdiagnosed initially. Doctors have an expression, “When you hear hoof beats, think of horses not zebras”. This maxim was invented in the late 1940’s by Dr. Theodore Woodward who was a professor at the University of Maryland School of Medicine.

Dr. Woodward was telling his medical students don’t assume an exotic medical diagnosis is likely when a more common explanation is available. Undoubtedly this is sound advice, but in the case of mesothelioma, perhaps more doctors should consider the sound of zebras. In fact, many doctors understand that “zebra-type” diagnoses should be considered until the evidence conclusively rules them out.

Mesothelioma occurs in about 2,000 patients a year in the U.S. It is an excellent example of a “zebra-type” diagnosis. Perhaps because of this, there have been mesothelioma patients who have had a misdiagnosis or delay in diagnosis because doctors assumed the hoof beats were from horses and were unwilling to consider an alternative explanation.

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