OBJECTIVETo elaborate on the clinical and pathologic features of sarcomatoid malignant mesothelioma (SMM), its diagnostic criteria and differential diagnoses.

METHODSTwenty-two cases of SMM retrieved from in-house and consultation files (between January 2009 to September 2013) were reviewed with emphasis on the clinicopathologic characteristics, immunophenotypes and the prognostic impact.

RESULTSThe mean age of the patients was 54 years (ranged from 24-73 years). There was no sexual predilection and the majority of the patients did not have history of asbestos exposure. Overall, 14 tumors developed in the pleura and 8 cases arose from the peritoneal cavity. Clinically, patients presented signs and symptoms in accord with the location of the tumors, notably coughing, shortness of breath, and chest pain for patients with pleural origin, and nausea, abdominal distention and abdominal pain for those with peritoneal primary. In most cases, CT and MRI scan demonstrated lobulated masses (8/11). However, diffuse infiltrative growth patterns were observed exclusively in a minority of pleural cases (3/11). No visceral lesion was observed in any case. Histologically, 19 cases had either fibrosarcomatous or undifferentiated pleomorphic sarcoma-like appearance. Two cases were consistent with desmoplastic mesothelioma. One case contained osteosarcomatous element. All cases expressed pan-cytokeratin (AE1/AE3), and most cases were also positive for D2-40 (15/20). The staining of calretinin (9/21) and WT1 (10/14) was generally weak and focal. They were all negative for TTF-1, napsin A, SP-A, p63 and CD34. Follow-up information (range from 1 to 36 months) was available in 11 cases, 6 of which were alive with unresectable tumor, 1 patient with recurrent disease and 4 patients succumbed to disease. The overall survival was 5 months (mean 8 months).

CONCLUSIONSThe diagnosis of SMM is achieved by comprehensive evaluation of medical history, imageological and pathological findings. Since calretinin immunoreactivity is infrequently observed in SMM, application of pan-cytokeratin and D2-40 immunostains offers a reasonable alternative for diagnosis. Diagnosis of SMM can be made by excluding a variety of spindle cell neoplasms with overlapping features, such as sarcomatoid carcinoma, synovial sarcoma, solitary fibrous tumor and fibrous pleuritis.