diagnosis of malignant mesothelioma

The diagnosis of malignant mesothelioma can be difficult, with symptoms and clinical
findings that can mimic and be mimicked by other diseases. Pleural mesothelioma
patients may present with dyspnoea, chest pain (pleuritic or non-pleuritic), cough
and weight loss, or any combinations of these symptoms (39-42). Initial clinical and
radiological examination usually reveals a pleural effusion, often massive. Rarely,
patients are asymptomatic at the time when a radiological abnormality is demonstrated,
and patients seldom present with metastatic disease.
Some patients with malignant mesothelioma experience a long interval between the
first onset of symptoms and subsequent diagnosis, but whether a long interval signifies
enhanced or diminished survival following diagnosis is unclear. Most patients with
malignant pleural mesothelioma have a background of asbestos exposure (40, 42), and
some may have had antecedent symptoms associated with benign asbestos-related
disease – for example, symptoms related to asbestosis or benign asbestos pleuritis with
effusion. Others may have radiological evidence of past asbestos exposure, such as
pleural plaques.

In general, biopsy, immunohistochemical analysis and correlation with radiological
and clinical features are needed for the diagnosis of mesothelioma (42). When
immunohistochemical findings are non-diagnostic or discordant, electron microscopy
– including electron microscopic examination of tissue retrieved from blocks of paraffinembedded
biopsy tissue or cytology cell blocks – can be used, but electron microscopy is
not recommended for ‘routine’ diagnosis of mesothelioma (21, 43).
Although several cytological and histological findings may raise varying levels of
suspicion of malignant pleural mesothelioma (see section 2.4) a current requirement
for the definitive clinicopathological diagnosis of malignant pleural mesothelioma is the
demonstration of neoplastic invasion – for example, infiltration into subpleural fat, chest
wall skeletal muscle, rib or lung – by histological examination or by imaging studies,
 and by clinical exclusion of alternative causes for an atypical mesothelial
proliferation.
A component of malignant mesothelioma in situ can be diagnosed when invasion has
been demonstrated in the same or different biopsy or by imaging studies (44). This
applies specifically to epithelioid malignant mesotheliomas. Sarcomatoid malignant
mesotheliomas are rarely diagnosable from effusion fluid cytology and are usually
identified histologically, by the demonstration of invasion or overtly sarcomatoid areas.