That conclusion, published in a recent issue of the British Journal of Cancer, is based on an analysis of more than 2,000 cases of malignant mesothelioma over 42 years.
Researchers from the University of Western Australia and Curtin University in Perth compared the survival rates and diagnostic methods used on mesothelioma patients in an effort to determine whether pathologists had correctly identified their subtypes. Their results suggest that they had, which is good news for patients.
Subtypes of Malignant Mesothelioma
There are three primary subtypes of malignant mesothelioma, an aggressive cancer usually caused by asbestos exposure. Epithelioid mesothelioma is the most common subtype, accounting for 50 to 70 percent of cases. It is also the subtype that is most responsive to treatment and carries the longest survival.
The least common but most aggressive and deadly mesothelioma subtype is sarcomatoid. An estimated 10 to 20 percent of mesothelioma patients have this subtype. Biphasic mesothelioma, which accounts for an estimated 20 to 35 percent of cases, contains both epithelioid and sarcomatoid cells.
Because mesothelioma subtype can only be determined by examining mesothelioma cells under a microscope, the Australian researchers wondered if it mattered whether those cells came from the lung fluid (which may contain fewer malignant cells) or from a biopsy of the mesothelioma tumor.
The answer is important because it is easier, safer, and less painful to collect a sample of excess lung fluid, called pleural effusion, than it is to obtain a tumor sample.
Mesothelioma Survival and Diagnostic Method
Out of the 2,024 mesothelioma cases evaluated for the study, 60 percent (1,212) were the epithelioid subtype. Of those, 41 percent had been diagnosed using the fluid cytology method alone.
Although the mesothelioma patients who were diagnosed with a lung fluid sample tended to be older than those who had had a biopsy, the median survival of the two groups was similar. This suggests that the cytology-only epithelioid diagnoses were accurate since missed cases of biphasic mesothelioma would likely have resulted in shorter survival times.
“Adjusting for age, sex, site and time since first exposure showed no difference in survival between the different diagnostic approaches,” writes study author Sanjeevan Muruganandan, MD, a respiratory medicine specialist at Sir Charles Gairdner Hospital in Perth.
The authors conclude that a diagnostic tap, a procedure used to remove a small amount of excess fluid, “should be considered adequate to diagnose epithelioid malignant mesothelioma without need for further invasive testing.”
An estimated 2,500 people are diagnosed with mesothelioma in the US each year. Most of them spent at least a portion of their work life in an industry where asbestos was used.
Muruganandan, S, et al, “Comparison of outcomes following a cytological or histological diagnosis of malignant mesothelioma”, February 14, 2017, British Journal of Cancer, Epub ahead of print