A new study of PET/CT for mesothelioma diagnosis shows that certain conditions can impact its accuracy. Test results may be less reliable in older patients and in those with very early stage mesothelioma.
The study comes from cancer researchers in Italy. They compared the accuracy of PET/CT for mesothelioma diagnosis in 141 patients over a 9-year period.
A third of the oldest patients with Stage 1 pleural mesothelioma received false negative results. The figure jumped to 40 percent when age was not considered.
What is PET/CT for Mesothelioma Diagnosis?
Positron emission tomography (PET) and computed tomography (CT) are non-invasive methods of looking at internal tissues.
A CT scan takes X-rays from different angles. A computer compiles the images into a 3-dimensional model. PET relies on a nuclear tracer called 18-FDG. The patient receives the tracer intravenously. Cancer cells absorb more of it (uptake) than healthy cells and a powerful magnet can detect that.
Examining mesothelioma cells in the lab is the only way to know for sure if a person has mesothelioma. But a combined PET/CT for mesothelioma diagnosis can help doctors confirm suspected cases.
Scanning Tool Has Limitations
Mesothelioma staging is the process doctors use to determine how far cancer has spread. Stage 1 mesothelioma tumors are small and confined to one area. In higher stages, cancer has spread to the lymph nodes or beyond. PET/CT for mesothelioma diagnosis can help with staging.
The current study included 141 mesothelioma patients diagnosed between 2009 and 2018 at two major medical centers. Patients were diagnosed pathologically as well as with PET/CT.
The overall detection rate using PET/CT for mesothelioma diagnosis was 88.3 percent. The rest of the study subjects had FDG uptake values below 2.5 percent, which is considered negative. But some of these negative results were wrong.
Thirty-three percent of older patients with Stage 1 mesothelioma received false negative results with PET/CT. Forty percent of all early stage mesothelioma tumors produced false negatives.
“PET-negative cases were more frequently detected in older patients and early-stage tumours,” writes study author Filippo Lococo.
Understanding the Subtleties of PET/CT
Clearly, PET/CT for mesothelioma diagnosis is not perfect. The team found that certain kinds of mesothelioma cells absorbed more tracer than others. Patients with epithelioid mesothelioma were more likely to have lower values than those with sarcomatoid or biphasic mesothelioma.
The Italian researchers conclude that doctors using PET/CT for mesothelioma diagnosis should be cautious.
“A low fluorodeoxyglucose uptake might be observed in more than 10% malignant pleural mesotheliomas, especially in early-stage tumours affecting elderly patients,” they write.
Mesothelioma patients who had the highest uptake values tended to have the worst prognosis.
Lococo, F, et al, “18F-fluorodeoxyglucose positron emission tomography in malignant pleural mesothelioma: diagnostic and prognostic performance and its correlation to pathological results”, January 31, 2020, Interactive Cardiovascular and Thoracic Surgery, Epub ahead of print, https://academic.oup.com/icvts/advance-article/doi/10.1093/icvts/ivz303/5718849