Straight Talk about Mesothelioma, a blog series created by Michael T. Milano, M.D., Ph.D., a radiation oncology specialist, as a resource for mesothelioma patients and their loved ones.

Researchers in Scotland recently published a study confirming that in patients with suspected pleural malignancy (i.e. with pleural fluid seen on an x-ray), routinely acquired CT scans are not precise enough to diagnose mesothelioma.

CT scans use a type of x-ray technology to create a 3-D image of the lungs and reveal possible mesothelioma lesions. Worrisome lesions seen on CT imaging would prompt a biopsy attempt to confirm the diagnosis. The problem is that often a CT scan will result in a false positive (in which a biopsy would reveal another condition) or false negative (in which a biopsy would not be attempted because CT is ‘negative’) for mesothelioma.

This rate of error suggests that doctors should perform pleural sampling and biopsy if they suspect a patient may have mesothelioma.

The study involved over 300 CT scans taken between January 2014 and April 2016, and analyzed the results of the scan versus the patient’s eventual diagnosis. While CT scans ruled out mesothelioma correctly in 80 percent of cases, they identified it correctly in only 58 percent of cases.

The scans that were examined by thoracic radiologists were more likely to lead to a correct diagnosis, yet the researchers concluded that the high likelihood of error means doctors cannot rely on CT scan alone.

The Difficult Diagnosis

Pleural mesothelioma is caused by asbestos exposure, a link that was found in studies as early as the 1960s. At that time, asbestos was still being widely used in construction materials and automobile parts such as brakes and clutches. While the health hazards became more widely known in 70s, this dangerous material still has not been banned in the United States.

Asbestos continues to be used in some consumer and construction products, and is often present in older buildings, so cases of mesothelioma persist.

Part of the problem in diagnosing mesothelioma is that it can take decades to develop, and the symptoms may not seem different from other respiratory ailments. People with mesothelioma may have problems with a persistent cough, chest pain, or trouble breathing. By the time those signs appear, however, the disease may have developed and spread extensively.

Combining Diagnostic Tests Is Best Tactic

The problem with relying on CT scans is that other conditions look very similar to mesothelioma on these scans, including diseases such as benign pleural plaques. Additionally, CT scans may not reveal small lesions, or they may suggest lesions are smaller than in reality.

Some medical centers have found that combining positron emission technology (PET) and CT scans can provide a more accurate picture of what is happening in the body. PET scans involve injecting a radioactively labelled sugar molecule that preferentially localizes to areas of the body where increased metabolic activity is happening. This metabolic activity suggests possible cancerous growth, which could be missed by CT scans. While CT scans are more accurate in showing where a growth might be, if there is low metabolic activity in that area, the mass could simply be scar tissue.

In short, the best scientific evidence to date suggests that while CT scans are a useful tool in the work-up of mesothelioma, they cannot be relied upon to be fully accurate. Ultimately a biopsy is the only way to diagnose mesothelioma, although the CT scan helps direct when and where to biopsy. When confronted with the possibility of a deadly disease such as mesothelioma, doctors and patients should consider PET scans and/or pleural sampling and biopsies in addition to CT scans.