Desmoplastic malignant mesothelioma originating from the peritoneum

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To the Editor, Malignant mesothelioma is an uncommon tumor arising in body cavities lined by mesothelium. Primary malignant peritoneal mesotheliomas make up 20–30 % of all mesotheliomas as represented by the total of pleural origin and are categorized into an epitheloid type. Desmoplastic mesothelioma categorized as a specific subtype of sarcomatoid mesothelioma is very rare and has a poor prognosis. Consequently, a peritoneal origin combined with desmoplastic histology is an extremely rare disease entity. A 74-year-old man presented to our hospital in February 2008 complaining of progressive abdominal distension due to an enlarging abdominal mass. Soluble interleukin-2 receptor was slightly elevated (452 U/mL) while the tumor markers examined were within the normal range. The tumor was rich in lipid content with an ill-defined border by contrast-enhanced abdominal CT scan (Fig. 1a) and magnetic resonance imaging (MRI) (Fig. 1b) the tumor was not enhanced but appeared to be originating from small bowel mesentery. It was difficult to make a definitive diagnosis of malignant lymphoma or mesenteric panniculitis without histological examination. Exploratory laparotomy revealed disseminated small white nodules in the mesentery (Fig. 1c) and the histology led to a pathologic diagnosis of desmoplastic mesothelioma, with a spindlelike shape based on collagenous fibers forming a storiform pattern (Fig. 1d). On immunohistochemistry, the tumor cells expressed vimentin, a smooth muscle actin, and D2-40 but tests for the following epithelial markers, calretinin, WT-1, desmin, CD34, and S-100 were negative (Fig. 1e–g). FISH analysis excluded a p16 deletion. Combination therapy based on either irinotecan (CPT-11) or gemcitabine (GEM) with cisplatin (CDDP) [1] was ineffective. We then gave CDDP intraperitoneally for 15 courses until we judged him to have unresponsive progressive disease. He was placed on optimal supportive care and survived for 49 months after the initial diagnosis. This is the first report on desmoplastic malignant mesothelioma of the peritoneum, since the disease entity was defined by the WHO in 2004. In an extensive review of the literature, we have identified only one previous report of this rare disease, published in 1982 [2]. The present patient is categorized as a diffuse mesothelioma based on the type of tumor spread. Generally, malignant peritoneal mesothelioma is considered to have a poor prognosis. Risk factors for malignant mesothelioma tumorigenesis are known to be an exposure to SV40 virus or to asbestos. The association of peritoneal mesothelioma with asbestos exposure is limited to a few cases and the associations authenticity is controversial. Regarding molecular mechanisms, somatic mutations of CDKN2A or NF2 or epigenetic alterations of RASSF1 gene promoter have been reported to be involved in tumorigenesis [3]. Currently, there are no established standard treatments for malignant peritoneal mesothelioma. Multidisciplinary strategies involving cyto-reductive surgery, systemic chemotherapy, and/or intraperitoneal chemotherapy as the present patient received have improved patient survival. Early diagnosis by exploratory laparotomy followed by combination chemotherapy may have contributed to longer survival for our patient than those of previous reports (median overall survival time for 20.1–26.8 months [1]). In conclusion, our patient highlights two important lessons; first, earlier intervention may contribute to longer H. Takamaru (&) Y. Arimura Y. Shinomura First Department of Internal Medicine, Sapporo Medical University, S-1, W-16, Chuo-ku, Sapporo 060-8543, Japan e-mail: h.takamaru@gmail.com