Mesothelioma Pathology - Incidence of Mesothelioma

Mesothelioma Pathology
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Incidence of mesothelioma.

Mesothelioma is a malignant tumor that originates in the pleura, peritoneum, pericardium and tunica vaginalis, all locations where a lining of normal mesothelial cell is present. According to the official data of Ministry of Health, Labor and Welfare in Japan, the number of death due to mesothelioma was 500 in 1995, increasing gradually to 953 in 2004. This increase appears to parallel the increase of the amount of asbestos imported into Japan between 1960 and 1975, given that the latent period from the beginning of exposure to asbestos and an initial diagnosis of mesothelioma is approximately 40 years.

More detailed examination of the 878 patients who officially died from mesothelioma in 2003 reveals that the male:female ratio was almost 3:1 and that the peak of age of patients was 60+ in males and 70+ in females. The location of the mesothelioma was in the pleura in 84% of the cases, in the peritoneum in 12% and in the pericardium in 1%; there were not cases of mesothelioma in the tunica vaginalis. A larger proportion of females had mesothelioma in the peritoneum and pericardium than in the pleura.

General findings on mesothelioma.

Mesothelioma can be roughly classified into localized and diffuse types, with the incidence of the latter being much higher than that of the former. The localized form of mesothelioma was more frequently diagnosed in the past; however, most of the localized forms are currently diagnosed as a solitary fibrous tumor, which is a separate entity from mesothelioma based on immunohistochemical phenotyping (positive for CD34, a marker of primitive endothelial cell) and has no relation to asbestos exposure.

At the early stage of pleural mesothelioma, small nodules are found in the parietal pleura (not in the visceral pleura) that eventually extend along the pleural surface. Eventually, parietal and visceral pleurae show adhesion, and the tumor encloses the entire lung parenchyma. Very few cases of peritoneal mesothelioma have been reported at the early stage and, consequently, little is known in terms of pathology and disease progression during the early stage. Most of peritoneal mesothelioma is found as a diffusely extensive tumor involving intestinal serosa or a large tumor located at the omentum or mesentery.

Following the initial diagnosis of mesothelioma, it is important to confirm the location of the tumor and its gross findings before histological examination. In the case of a pleural mesothelioma, a tumor in the lung parenchyma suggests lung cancer with a pleural extension. In females with peritoneal extension, the ovary should be carefully examined as the primary site of the tumor because the differential diagnosis between ovarian cancer and peritoneal mesothelioma is difficult and can only be made on the basis of histological analyses.

Histology of mesothelioma.

Histological classification of mesothelioma is shown. There are three major types—epithelioid type, sarcomatoid type and biphasic type—and the proportion of each is approximately 60, 20 and 20%, respectively. The desmoplastic type is rare (probably 1–2%), and special variants only appear sporadically (several percentages). However, the proportion of each histological type varies among the reports because of the large variety of histological analyses used.

Differential diagnosis.

It is important to remember that there are many diseases to be differentiated when making a pathological diagnosis and that the tissue to be differentiated varies in terms of histological type. Epithelioid types must be differentiated from lung adenocarcinoma for pleural mesothelioma, ovarian serous papillary adenocarcinoma or peritoneal serous carcinoma for peritoneal mesothelioma. In terms of sarcomatoid types, sarcoma originating in the chest wall, lung, pleura, abdominal wall, peritoneum and intestine must be excluded. Sarcomatoid carcinoma (spindle cell sarcoma or pleomorphic carcinoma) of the lung is very difficult to differentiate from sarcomatoid pleural mesothelioma. In terms of the biphasic type, carcinosarcoma or pulmonary blastoma of the lung, biphasic synovial sarcoma of the pleural mesothelioma and carcinosarcoma of the female genital organs must be differentiated from their peritoneal counterpart. The desmoplastic type has a similar histology to fibrous pleuritis, and the differential diagnosis is very difficult, particularly if only a small biopsy specimen is available.

Mesothelioma Pathology - Incidence of Mesothelioma
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🔗 https://www.ncbi.nlm.nih.gov/p....mc/articles/PMC26982

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