Page 522 - Textbook of Pathology, 6th Edition

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Figure 17.42 Malignant mesothelioma, showing biphasic pattern
of growth.

Microscopically, malignant mesothelioma may have
epithelial, sarcomatoid or biphasic patterns.
Figure 17.41 Malignant (diffuse) mesothelioma, gross appearance.
The tumour is seen to form a thick, white, fleshy coat over the parietal i) Epithelial pattern resembles an adenocarcinoma,
and visceral surfaces.
consisting of tubular and tubulo-papillary formations. The
tumour cells are usually well-differentiated, cuboidal,
osteoarthropathy or hypoglycaemia. Removal of the tumour flattened or columnar cells.
is generally curative. ii) Sarcomatoid pattern consists of spindle cell sarcoma
resembling fibrosarcoma. The tumour cells are arranged
Malignant (Diffuse) Mesothelioma in a storiform pattern with abundant collagen between
SECTION III
them.
Malignant or diffuse mesothelioma is rare. It is a highly
malignant tumour associated with high mortality. The iii) Biphasic pattern shows mixed growth having
tumour is significant in view of its recognised association with epithelial as well as sarcomatoid pattern. Usually, there
occupational exposure to asbestos (particularly crocidolite) for are slit-like or gland-like spaces lined by neoplastic
a number of years, usually 20 to 40 years (page 492). About mesothelial cells separated by proliferating spindle-
90% of malignant mesotheliomas are asbestos-related. shaped tumour cells (Fig. 17.42).
Mechanism of carcinogenicity by asbestos is not quite clear Asbestos bodies are found in the lungs of most patients
but it appears that prolonged exposure of amphibole type of with malignant mesothelioma of any histologic type.
asbestos is capable of inducing oncogenic mutation in the Clinical manifestations include chest pain, dyspnoea,
mesothelium. However, prolonged asbestos-exposure is pleural effusion and infections. The tumour spreads rapidly
considered more significant rather than heavy exposure as by direct invasion into lung and by lymphatic spread into
Systemic Pathology
documented by occurrence of malignant mesothelioma in the hilar lymph nodes and pericardium. Sometimes distant
family members of asbestos workers. Although combination metastases, particularly to the liver, occur. The prognosis is
of cigarette smoking and asbestos exposure greatly increases poor; 50% of patients die within one year of diagnosis.
risk to develop bronchogenic carcinoma, there is no such
extra increased risk of developing mesothelioma in asbestos
workers who smoke. Recently, SV40 (simian vacuolating SECONDARY PLEURAL TUMOURS
virus) antigen has also been implicated in the etiology of Metastatic malignancies in the pleura are more common than
mesothelioma. the primary tumours and appear as small nodules scattered
over the lung surface. The most frequent primary malignant
Grossly, the tumour is characteristically diffuse, forming tumours metastasising to the pleura are of the lung and breast
a thick, white, fleshy coating over the parietal and visceral through lymphatics, and ovarian cancers via haematogenous
surfaces (Fig. 17.41). route.

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