The influence of the diagnostic technique on the histopathological diagnosis in malignant mesothelioma

In the histopathology of malignant mesotheliomas three different types (epithelial, connective tissue and mixed type) are distinguished. Some authors believe all tumours to be of mixed type, but consider that due to inadequate sampling or small biopsies this may be missed frequently. In this study the relationship between the histopathological diagnosis and the amount of tissue examined was investigated. In a series of 124 cases of malignant pleural mesothelioma a high percentage of mixed type tumours was found (55%). In cases where the decisive diagnostic procedure had been an Abrams biopsy (the "small-specimen" technique) mixed-type histology was found in 36%. If thoracoscopy, thoracotomy or autopsy (the "large-specimen" techniques) had delivered a definite diagnosis, mixed-type histology was found in 63%. Apparently diagnosing the mixed-type variety depends on the amount of tumour tissue obtained. However, the assumption that all mesotheliomas are of mixed type cannot be confirmed

The malignancy grading method is not a reliable assessment of malignancy in mesothelioma

The ploidy of a series of pleural lesions--reactive proliferations, malignant mesotheliomas and metastatic tumours--was measured on a Leitz Miamed DNA image analyser using Feulgen-stained slides. The technique successfully recognized all the metastatic tumours as malignant; this corresponds to previous work. However, it was not successful in classifying mesothelial lesions as benign or malignant, resulting in a very high false-negative rate and a moderately high false-positive rate. Mesothelial lesions appear to have a wide range of ploidy values irrespective of their biological behaviour. Thus, for primary mesothelial tumours, the ploidy value cannot be used as a reliable diagnostic index