CONTENTS:

5.10 Mesothelioma Lung Cancer
5.10.1 Asbestos Exposure and Mesothelioma
5.10.2 Diagnosis of Mesothelioma Lung Cancer
5.10.3 Variants of Mesothelioma
i. Epithelioid Mesothelioma
ii. Sarcomatoid Mesothelioma Lung Cancer
iii. Biphasic (Mixed) Mesothelioma

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5.10 Mesothelioma Lung Cancer

Mesothelioma lung cancer is a malignant tumor of the mesothelial cells that are found on the surfaces of the pleural and peritoneal cavities, or the pericardium.

80 % of all cases of mesothelioma lung cancer are pleural in origin.

5.10.1 Asbestos Exposure and Mesothelioma Lung Cancer

Patients who develop mesothelioma have an occupational history of asbestos exposure, such as miners, engineers, and construction-workers. The cause of mesothelioma lung cancer is inhaled or ingested asbestos fibers.   Women who have a history of washing clothes of a family member who worked with asbestos also are a risk of developing mesothelioma.

From first exposure to asbestos, to developing mesothelioma, the time interval is virtually never less than fifteen years and peaks at 30 to 40 years.

Mesothelioma lung cancer is still a relatively rare tumor, although reported incidence rates have increased in the past 20 years. The incidence rate varies worldwide, with the highest rates in Australia, Britain, and Belgium (30 cases per 1,000,000 per year). In the U.S., the incidence is thought to have peaked at 15 per 1,000,000 in 2004. The incidence of mesothelioma is expected to continue increasing in other parts of the world.

Mesothelioma occurs more often in men than in women; the risk increases with age.  Mesothelioma represents less than 1% of all cancers diagnosed in the U.K., where it is the 17th most common overall cause of cancer death.

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5.10.2 Diagnosis of Mesothelioma

The diagnosis of mesothelioma is difficult to make, and this is for a variety of reasons.

• Firstly, in many cases, there is only a limited amount of tissue available for histopathology. The use of video-assisted thoracoscopy (VAT) biopsies has greatly improved the size of pleural biopsies.
• Second, malignant mesothelioma can vary greatly in histologic appearance, even within one patient.
• Third, a number of other tumors can mimic malignant mesothelioma histologically.
• Fourth, there are a number of benign pleural diseases that may be difficult to separate from pleural mesothelioma.

The use of immunohistochemistry (IHC) has improved the accuracy of diagnosis and molecular studies, can also improve diagnostic accuracy in certain situations. A thorough clinical history should include knowledge of any prior history of malignancy, and high-quality radiographic studies contribute to the histopathologic diagnosis.

Early-stage malignant pleural mesothelioma presents as multiple small nodules that coalesce to form a thickened rim of tumor that fuses the parietal and visceral pleural surfaces.

Advanced mesothelioma encases the entire lung and extends along the interlobar fissures, with a tumor consistency that varies from firm to gelatinous.  Adjacent structures can be involved at an early stage, with tumor invasion of the chest wall, pericardium, and diaphragm.

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Figure 5.7 Mesothelioma.

A. Macroscopic appearance of the lung affected by mesothelioma, shows thickened,
white pleura surrounding the lung.  B. Photomicrograph of lung contains asbestos
fibers, covered in brown iron deposits (‘ferruginous bodies’). (H&E x60).
C. Photomicrograph of the histology of the mesothelioma, epithelioid variant.
(H&E x40)

5.10.3 Variants of Mesothelioma Lung Cancer

Malignant mesothelioma is classified into three histologic subtypes – epithelioid, sarcomatoid, and biphasic (mixed).

i. Epithelioid Mesothelioma

The epithelioid variant is the most common (60 % of all mesotheliomas).  Histologic appearances of this subtype include tubulo-papillary, acinar (glandular), adenomatoid and solid epithelioid patterns. In this subtype, the differential diagnosis includes metastatic carcinomas and other epithelioid tumors.

Sarcomatoid Mesothelioma

Sarcomatoid mesotheliomas contain malignant spindle cells and so may mimic malignant mesenchymal tumors, such as leiomyosarcoma. ‘Desmoplastic mesothelioma,’ which consists of bland tumor cells between dense bands of collagen, is now considered to be a subtype of sarcomatoid mesothelioma. The differential diagnosis includes fibrous pleurisy, sarcomatoid carcinoma, and other sarcomas.

iii. Biphasic (Mixed) Mesothelioma

Biphasic or mixed mesotheliomas have epithelioid and sarcomatoid features. Multiple tissue sections or larger samples may be needed to demonstrate both components. Synovial sarcoma, as well as other mixed or biphasic tumors, are typically considered in this differential diagnosis.

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References:

Allen TC. (2005). Recognition of histopathologic patterns of diffuse malignant mesothelioma in differential diagnosis of pleural biopsies. Arch Pathol Lab Med 129(11), 1415. (Retrieved 12^th Feb 2015)

Hammar SP. (2006). Macroscopic, histologic, histochemical, immunohistochemical, and ultrastructural features of mesothelioma. Ultrastruct Pathol. 30(1), 3. (Retrieved 10^th Feb 2015)

More references for this section are on this page.

Patient Information:

Health and Safety Executive (HSE) Asbestos FAQ’s (Retrieved 22^nd Jan 2015): http://www.hse.gov.uk/asbestos/faq.htm

Mesothelioma Lung Cancer Guide. com   (Retrieved 12^th Feb 2015): http://www.mesotheliomaguide.com/mesothelioma/causes/

More patient information for this section is on this page .

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