Transmission electron microscopy — a high-resolution method to explore cell characteristics — can aid in the diagnosis of malignant pleural mesothelioma when examining cells found in the liquid surrounding the lungs.
But the method may be hampered by the fact that only slightly more than half of liquid samples contain cells that can be used for diagnosis.
The study, “Diagnostic efficacy of electron microscopy and pleural effusion cytology for the distinction of pleural mesothelioma and lung adenocarcinoma,” was published in the journal Ultrastructural Pathology.
For oncologists, discriminating between mesothelioma and lung adenocarcinoma is not always straightforward. For a positive mesothelioma diagnosis, a pathologist explores a tissue sample under the microscope. A collection of antibody stains, examined under a light microscope, can visualize cell structures that differ between the two cancer types.
Electron microscopy is already in use to aid the diagnosis of mesothelioma, when light microscopy analysis is inconclusive. But the tissue samples needed for this type of analysis need to be of high quality.
In patients with cancer involving the lungs, liquid often accumulates outside the lungs — a feature called pleural effusion. Since many patients have a pleural effusion biopsy taken as the only tissue sample, researchers from the Instituto Nacional de Cancerologia in Mexico decided to study whether cells from the liquid can be used instead of traditional tissue samples.
In 25 pleural samples taken from five mesothelioma and 20 adenocarcinoma patients, they identified structures that differed between the two cancer forms.
The team showed that microvilli — tiny moving protrusions that help the lungs to expel dust, mucus, and microbes — had particular features in the two cancers.
Mesothelioma cells had long, thin microvilli that lacked the outermost layer — called the glycocalyx — needed for the attachment of substances to the protrusions. In contrast, the structures were short with an intact outer layer in adenocarcinoma.
The main limitation of the method was that the team only found cells in 60 percent of the samples from mesothelioma patients, and in 55 percent of lung cancer samples.
In an invited commentary, published in the Journal of Thoracic Disease, two researchers from Tor Vergata University of Rome in Italy argue that the study reveals new possibilities to use electron microscopy in cases where it is impossible to distinguish between the cancer types using conventional methods only.
They underscore that the method, using pleural effusion cells, may be particularly useful in patients for which tissue samples cannot be obtained or are not of sufficiently good quality for standard electron microscopy methods.
But considering the small number of patients in the study, they emphasized the need for further studies to validate the characteristics linked to mesothelioma.