Researchers at Case Western Reserve are warning cancer doctors not to rely too heavily on PET/CT scans when diagnosing malignant mesothelioma – especially in older patients.
PET/CT is an important tool for staging mesothelioma and can help with diagnosis. But a new case report highlights the problem of false-negative PET/CT scans.
In this case involving a 77-year-old man, PET/CT showed no mesothelioma. Even the man’s lung fluid tests were negative for mesothelioma. The case is a potent reminder that biopsy is still the gold standard for diagnosing asbestos cancer.
PET/CT Scans and Other Tools for Diagnosing Mesothelioma
Pleural mesothelioma is a tricky cancer to diagnose. Most patients do not even have symptoms until the disease is in a later stage. If they do have symptoms, they may be vague like coughing or fatigue.
Doctors use a variety of tools to diagnose mesothelioma. The first one is patient history. Since asbestos is the number one cause of mesothelioma, having a history of asbestos exposure is the first red flag.
PET/CT scans, MRI images, blood tests, lung fluid tests, and biopsies are other diagnostic tools for mesothelioma.
PET stands for positron emission tomography. It uses a radioactive tracer to measure the metabolic rate of cells. Cancer cells tend to absorb more of the tracer than normal cells. They show up as bright spots on PET/CT scans.
The Danger of False Negative Results
The Case Western Reserve University case report shows why it can be dangerous to rely on PET/CT scans for mesothelioma diagnosis.
The 77-year-old patient had shortness of breath. His doctors found fluid and air in the pleural space around one of his lungs and suspected that he might have cancer.
They removed some of the fluid and examined it under a microscope. This is a technique that often shows early evidence of mesothelioma. But there were no signs of cancer.
The man then underwent PET/CT scans with a tracer called FDG. There were still no signs of mesothelioma. It was not until doctors performed a biopsy and looked at the man’s tissue under the microscope that they were able to confirm pleural mesothelioma.
The team concluded that the man’s age probably affected his metabolic rate. The fact that his tumor was small might also account for the false-positive scan results. The results are similar to those of a 2020 study on PET/CT scans and mesothelioma.
“Older patients with early stage MPM are more likely to have false-negative FDG PET/CT results,” writes author Haley Corbin of Case Western Reserve University School of Medicine. “Pleural biopsy is essential when there is clinical suspicion for mesothelioma, even with negative initial FDG PET imaging.”
About 2,500 Americans receive a diagnosis of mesothelioma each year. The earlier the illness is diagnosed, the better the chances of survival.
Corbin, H and Packer, C, “False-Negative 18F-Fluorodeoxyglucose PET/CT in Malignant Pleural Mesothelioma”, August 17, 2021, Cureus, Peer Reviewed Case Report, https://www.cureus.com/articles/64800-false-negative-18f-fluorodeoxyglucose-petct-in-malignant-pleural-mesothelioma