Abstract
This report describes a rare case of localized malignant biphasic (mixed epithelioid and sarcomatoid) mesothelioma arising in the peritoneum. A 69-year-old male with a history of asbestos exposure, complaining of a painful mass in the left chest wall, was found via computed tomography (CT) to have a tumor in the left peritoneum. The resected tumor was histologically and immunohistochemically consistent with a malignant mesothelioma with mixed epithelioid and sarcomatoid type and no distant metastasis. The diagnosis of localized malignant biphasic mesothelioma arising in the peritoneum was appropriate because there was no evidence of any other primary tumor.
Keywords: Immunohistochemistry, localized mass, mesothelioma, peritoneum, surgical resection
Introduction
Malignant mesothelioma is the most common primary tumor of the serosal membrane of the pleura, peritoneum, and pericardium. Most cases of malignant mesothelioma present with an obviously diffuse tumor, and the presence of a grossly visible diffuse tumor is usually cited as an important criterion for making the diagnosis. In contrast, Allen et al. have recently reported a series of localized malignant mesotheliomas as uncommon sharply circumscribed tumors of the serosal membranes with the microscopic appearance of diffuse malignant mesothelioma.1 They proposed that localized malignant mesotheliomas should be separated from diffuse malignant mesotheliomas because of their localized presentation, quite different biological behavior, and far better prognosis. This report presents a case of unsuspected malignant mesothelioma of the peritoneum presenting as localized mass on the left anterolateral abdominal wall. There has been previously only one case report describing localized biphasic type malignant peritoneal mesothelioma.2
Case report
A 69-year-old male, with a history of asbestos exposure, presented with a painful mass in the left chest wall lasting for a period of six months, gradually increasing in size. He was admitted to the hospital for an investigation of the mass. A painful and immovable mass, which measured about 5 cm in diameter, was felt on the left lateral chest wall. All other clinical parameters were within the normal ranges. Computed tomography (CT) showed the presence of a 7.1 cm tumor mass on the left anterolateral abdominal wall (Fig 1). The solitary circumscribed mass extended under the skin and into the peritoneal cavity, and was suspected to directly invade the adjacent rib bones and transverse colon. The marginal region of the mass was enhanced by contrast medium. A simple excision of the left anterolateral abdominal wall mass and reconstruction of the diaphragm and peritoneum were performed. On observing the left thoracic and peritoneal cavities using a thoracoscope, neither pleural and peritoneal dissemination nor effusion was found. The tumor was resected en bloc with two ribs, the diaphragm, parietal peritoneum, and an adequate margin free from the tumor. Direct invasion of the transverse colon was suspected on imaging, but the tumor invaded only the omentum. The involved omentum was resected with a margin that was macroscopically free of the tumor invasion. The defects of the diaphragm and parietal peritoneum were repaired with Goretex dual Mesh (W.L. Gore & Associates, Inc., AZ, USA). The patient had an uneventful postoperative recovery without any complications.
Figure 1.
Computed tomography (CT) of the chest and abdomen demonstrated the presence of a 7.1 cm tumor mass on the left anterolateral abdominal wall.
The excised left anterolateral abdominal wall tumor (Figs 2 & 3) was 10.7 × 6.0 × 6.2 cm in size and weighed 200.4g after formalin fixation. Its cut surface showed an ill-defined whitish tumor with massive necrosis in the center, and the tumor included the rib bones. The histological specimens showed massive and geographic coagulation necrosis in the center and viable tumor cells locating at the periphery. There were polygonal and spindle-shaped tumor cells with thick eosinophilic cytoplasm and a large nucleus. The nucleoli were prominent. Such tumor cells proliferated in interlacing and epithelioid patterns. Mitotic figures were also occasionally encountered.
Figure 2.
Macroscopic findings. The excised left anterolateral abdominal wall tumor was 10.7 × 6.0 × 6.2 cm in size and weighed 200.4g after formalin fixation. Its cut surface showed an ill-defined whitish tumor with massive necrosis in the center, and the tumor included the rib bones.
Figure 3.
Histological examination (a: Hematoxylin and eosin (H&E) stain, b: calretinin immunostain). (a) Low magnification of the tumor. It shows massive necrosis in the left half and mixed sarcomatoid and epithelial mesothelioma in the right half. Three rib bone fragments can be found in the left side (H&E 4×). The insert at the right upper corner shows a high power view of the viable spindle shaped tumor cells in an interlacing pattern (H&E 20×). (b) The tumor cells showed a positive reaction to calretinin (40×).
Immunohistochemically, those tumor cells showed a strong positive reaction to vimentin, pancytokeratin (PanCK) and cytokeratin 7 (CK7), a weak positive reaction to calretinin and CK5/6, and a negative reaction to Wilms tumor 1 (WT-1) and D2-40. There were localized CD68 positive cells. In addition, those tumor cells showed a completely negative reaction on HMB-45, Ber-EP4 and cytokeratin 20 (CK20) (Table 1). An Elastica van Gieson stain (EVG) showed an uncertain venous permeation. The tumor cell characteristics that were consistent with the localized form of malignant mesothelioma included vimentin (++), calretinin (+), PanCK (++), CK7 (++), CK5/6 (+), Ber-EP4 (-) and CK20 (-), but not on D2-40 (-) and WT-1 (-).
Table 1.
Immunohistochemical findings of the present case
| Antibody | Reaction |
|---|---|
| Vimentin | ++ |
| PanCK | ++ |
| CK7 | ++ |
| Calretinin | + |
| CK5/6 | + |
| WT-1 | – |
| D2-40 (podoplanin) | – |
| CD68 | + |
| HMB-45 | – |
| Ber-EP4 | – |
| CK20 | – |
++, strong positive; +, weakly or focally positive; –, negative.
CK5/6, cytokeratin 5/6; CK7, cytokeratin 7; CK20, cytokeratin 20; PanCK, pancytokeratin; WT-1, Wilms tumor 1.
A total body exam was performed to determine if there were any additional primary tumors. He underwent fluorodeoxyglucose positron-emission tomography (FDG-PET) after surgery, but there was no evidence of an abnormal accumulation that would indicate a primary tumor or distant metastasis. The diagnosis of localized malignant mesothelioma arising in the peritoneum was appropriate. We considered adjuvant therapy according to diffuse malignant mesothelioma, but the patient was followed closely without therapy because he has had angina and cardiac depression and the tumor was localized. He has been doing well without recurrence for seven months after surgery.
Discussion
Localized malignant biphasic peritoneal mesothelioma is very rare. Localized malignant mesothelioma is an uncommon circumscribed tumor of the serosal membrane with the microscopic appearance of diffuse malignant mesothelioma, but without any evidence of infiltration. Allen et al. reported 23 cases of localized malignant mesothelioma. The origin of the 21 tumors was pleural and two were peritoneal. Sixteen tumors revealed microscopic patterns of diffuse epithelial mesotheliomas, six had mixed epithelial and sarcomatous patterns, and one was purely sarcomatous. Ten of the 21 patients with follow-up data survived without evidence of disease from 18 months to 11 years after diagnosis and surgical excision of the tumor. Patients who died had developed local recurrences and metastases, but none had diffuse pleural spread. Localized malignant mesotheliomas should be separated from diffuse malignant mesothelioma because of their localized presentation, quite different biologic behavior, and far better prognosis.1 Clinical reports of localized peritoneal mesothelioma show that the epithelioid type predominates,1,3 very few tumors are biphasic (mixed epithelioid and sarcomatoid) type,2 and there has been no previous case report of the purely sarcomatoid type. The current case is the second report of localized peritoneal biphasic type mesothelioma (Table 2). Biphasic malignant mesotheliomas contain both epithelioid and sarcomatoid areas within the same tumor. While epithelioid and sarcomatous types can be seen in peritoneal malignant mesothelioma, the incidence of biphasic tumors is lower than in pleural disease, and pure sarcomatous tumors are very rare.4
Table 2.
Documented cases of localized biphasic type malignant mesothelioma arising in the peritoneum
| Author | Year | Age (years) | Sex | Site | Asbestos history | Follow-up | Pathology to dominant |
|---|---|---|---|---|---|---|---|
| Matsukuma et al.2 | 1996 | 68 | Male | Abdominal wall near the liver | No | Died 10 months after the initial surgery | Sarcomatoid |
| Present case | 2012 | 69 | Male | Left anterolateral abdominal wall | Yes | No recurrence over the seven months after the surgery | Biphasic instead of half |
Malignant mesothelioma should, therefore, be included in the differential diagnosis of primary left anterolateral abdominal wall tumor, especially in patients with a history of asbestos exposure. A very careful histological and immunohistochemical examination was required to reach the definite diagnosis in the present case, because of the unusual localization of the tumor. The diagnosis of localized malignant mesothelioma can only be distinguished pathologically in a localized pleuroperitoneal mass via CT and confirmed by localized uptake with FDG-PET. PET imaging has increased recognition of mesothelioma. Bénard et al. reported 91% sensitivity and 100% specificity for the differentiation of malignant and benign pleural diseases, and epithelial subtype tended to have low metabolic uptake using the quantitative standardized uptake value (SUV).5 Others have concluded that PET does not depict the local extent of mesothelioma, but is valuable for the identification of extrathoracic metastases.6 Malignant mesothelioma exhibits a high resistance to chemotherapy and only a few patients of diffuse malignant mesothelioma are candidates for radical surgery.7 The crucial feature of localized malignant mesothelioma is that many cases can apparently be cured by surgical excision. Therefore, such patients should undergo a whole body exam using, for example, FDG-PET, to identify any primary tumor when a tumor arises in the pleuroperitoneum. In addition, an aggressive and complete tumor resection should be performed if the tumor is considered to be the primary tumor.
Acknowledgments
We thank Dr. Brian Quinn for critical comments on the manuscript.
Disclosure
No authors report any conflict of interest.
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