Establishing a Diagnosis of Mesothelioma
Mesothelioma grows slowly, and silently. For ten years, sometimes for as long as 40 years the tumor grows within the body, causing no symptoms. Only when it has grown large enough to press on vital organs, or to leak fluid into the chest or abdominal cavity does the victim begin to experience symptoms such as severe chest pain, shortness of breath, and constant fatigue.
Diagnostic Inclusion
Mesothelioma diagnosis involves several challenging tasks. The first task is diagnostic inclusion. Because mesothelioma is not a common illness, it is not usually a primary suspect. This is a problem because by the time mesothelioma causes symptoms, it is well advanced, and the time remaining in which the disease can be treated is already limited. It is important to alert a diagnosing physician to any previous asbestos exposure, so that the physician is sure to include mesothelioma as a possible diagnosis.
Non-invasive Imaging
If mesothelioma is suspected, the second task is to evaluate the likelihood of its presence, using non-invasive imaging techniques. A definitive mesothelioma diagnosis is established by tissue biopsy, an invasive surgical procedure which removes a piece of the suspected tumor for evaluation by a pulmonary pathologist. Because this procedure carries some measure of risk for the patient, a physician is reluctant to order it unless there is a high degree of suspicion that a tumor is present.
Several imaging techniques can provide information. An X-Ray can show the existence of mass, and in the lungs, the presence of fluid. The X-Ray cannot confirm whether the mass is a tumor.
The Computed Tomography or CT scan takes a large series of X-Ray cross sections through the body, which are integrated by computer into a very detailed 3-dimensional view of the body. They can show thickening of the mesothelium, but a CT scan alone cannot definitively diagnose mesothelioma.
Additional information can be gained from a PET scan. Positron Emission Tomography involves injecting a small amount of radioactive glucose into the bloodstream, and studying where in the body the glucose is most actively consumed. A tumor is an area of extremely high cell growth and reproduction. It will consume a disproportionate amount of the glucose, and show on the scan as a "hot spot," an area of high activity. A PET scan shows hot spots, but is imprecise about location.
These two scans can now be combined. In the resulting image, the PET scan can show a suspicious area whose high metabolic activity suggests a tumor, and the CT scan contributes more detailed information about the areas size, shape, and precise location. This integrated scan gives the best information available without an invasive procedure, and enables the diagnosing physician to make a judgment about whether to proceed with a surgical biopsy.
Fluid Removal, Thoracentesis
Early in the diagnostic process, fluid may be removed from the chest cavity, a procedure called thoracentesis. Although the principal aim of this procedure is pain relief by reducing the fluid's pressure on the lungs, the fluid is also studied for the presence of discarded tumor cells, which may or may not be found in the fluid. A reliable mesothelioma diagnosis from the fluid can be made only in about a third of cases.
Surgical Biopsy
If the imaging studies indicate a high likelihood of a mesothelioma, the next step is a surgical biopsy, conducted under general anesthesia. An increasing number of procedures are performed endoscopically, in which several small incisions are made in the chest or abdomen rather than a single large one.
In a thorascopy, a biopsy of the chest cavity, the lung with the suspected tumor involvement is deflated, to allow room between it the chest wall for the surgeon to work. The incisions are made between the ribs. Making the incisions there reduces potential damage to nerves, muscles, and to the ribs themselves. An endoscope, a slender, flexible fiber optic tube with a video camera is inserted through one incision, and instruments for removing a tissue sample are inserted through another. Working from the image on a video monitor, the surgeon removes a piece of the suspected tumor. Then the instruments are removed, the incisions closed, and the lung re-inflated.
For an abdominal biopsy, also called a laparoscopy, the procedure is similar. The incision is usually made at the navel. A hollow needle is inserted into the abdominal cavity, and carbon dioxide gas is pumped into the abdomen to expand it. The expansion enables the surgeon to see the organs more clearly. The laparoscope with video camera is inserted through one incision, and the biopsy instruments through another. The tissue sample is removed, the instruments withdrawn, and the incisions are closed.
Pathology Exam
A pulmonary pathologist, a specialist in examining lung tissue, will study the biopsy specimen microscopically to determine the kinds of cells it contains, the structure of those cells, and their response to a number of specialized chemical and immunological tests. The pathologist's findings are the most reliable and specific diagnostic understanding of the disease and its progression. This information is essential in planning a course of treatment.
Biological Markers
One of the most promising areas of research in mesothelioma diagnosis is the development of a blood test for evaluating the status and progress of mesothelioma tumors. Two different proteins, Serum Mesothelin Related Protein (SMRP), and Osteopontin have been found to be present in higher levels in the blood of people with mesothelioma and other cancers.
As of January 2007 Fujirebio Diagnostics has received permission from the U.S. Food and Drug Administration, FDA, to market its Mesomark® Assay, which measures SMRP. Use of the assay will enable treating physicians to better approximate the volume of a tumor, and to calibrate dosage for chemotherapy. It will also be used to evaluate mesothelioma patients' response to surgery and other treatments, and to monitor for possible recurrences of the disease. Fujirebio plans further research toward the use of Mesomark to detect the presence of mesothelioma.
Osteopontin, a protein first identified in 1986, also appears to have potential as a marker to indicate disease progress and response to treatment.
