Xanthomatous pleuritis mimicking mesothelioma.

Recurrent non-malignant exudative effusions remain a diagnostic and potentially management dilemma. Fluid characteristics frequently narrow the differential but fail to offer a definitive diagnosis. Medical thoracoscopy is well tolerated and allows direct visualization and biopsy of pleural processes under conscious sedation. Rarely, macroscopic appearance and even histology may be misleading. We present a case of xanthomatous pleuritis that mimicked early mesothelioma. Our patient was a 69-year-old female with a large left pleural effusion. Her medical history was significant for a recent small pericardial effusion without cardiac dysfunction. Thoracentesis revealed a non-malignant exudative effusion. Thoracoscopy demonstrated two foci of raised soft plaques with petechial hemorrhage and adhesions. Preliminary evaluation suggested chronic inflammation admixed with proliferating spindle cells and necrosis. The immunohistochemical phenotype of the spindle cells favored a spindle and epithelioid cell neoplasm, mesothelioma. Because of discord between pathologists, we repeated the thoracoscopy through the existing chest tube/thoracoscopy site. We acquired more tissue for special stains and outside review. Following extensive immunohistochemistry, the diagnosis of xanthomatous pleuritis was made. Our patient quickly recovered with steroid therapy and is without recurrence 18 months later. This case demonstrates the utility and nuances of medical thoracoscopy in a perplexing case of xanthomatous pleuritis.

Desmosomes and microvilli mean a lot: diagnosis of neoplasms of unknown origin using electron microscopy.

Neoplasms of unknown origin present a difficult diagnostic dilemma, particularly if they are very poorly differentiated. Adenocarcinomas, squamous cell carcinomas, melanomas, lymphomas, and sarcomas can all be very difficult to diagnose if the light microscopic cytomorphology is sufficiently undifferentiated. Electron microscopy (EM) can either demonstrate differentiation or narrow the range of differential diagnoses. The authors report the case of a 64-year-old male who has been HIV positive for several years and was found to have expansile lytic lesions in several ribs and a thumb fracture associated with a soft tissue mass which was biopsied. The tumor was composed of very pleomorphic malignant cells without specific differentiation. The malignant cells stained positive for pancytokeratin (AE 1/3), EMA, CEA, CK20, and CK7. Rare cells had mucicarmine-positive intracytoplasmic droplets. They were negative for S-100, calretinin, CD45, MART-1, and vimentin. EM revealed intracytoplasmic lumina with long microvilli and many well-formed desmosomal junctions. The diagnosis was initially very broad. Immunohistochemistry narrowed the diagnosis to carcinoma, but EM alone was able to narrow the diagnosis to poorly differentiated adenocarcinoma. In a neoplasm of unknown origin, EM can either narrow the differential significantly or, in the case of limited material, provide information that otherwise may not be attainable.

The spectrum of immunohistochemical reactivity of monoclonal antibody DS6 in nongynecologic neoplasms.

DS6 is a murine monoclonal antibody that was developed using ovarian serous adenocarcinoma as immunogen. DS6 reacts immunohistochemically with a tumor-associated antigen, CA6, which has only a limited range of expression in normal human tissues. CA6 is most characteristically expressed in type II pneumocytes, fallopian tube epithelium, and urothelium, but lacks expression in mesothelium. The authors recently reported the spectrum of reactivity of DS6 with a wide variety of neoplasms of the gynecologic tract and found DS6 to be highly characteristic of serous neoplasms. CA6 is also expressed in other müllerian-derived epithelial neoplasms of the gynecologic tissues, but is not typically expressed by ovarian intestinal-type mucinous neoplasms, mesothelioma, mesenchymal neoplasms, ovarian germ cell tumors, or sex cord-stromal neoplasms. In this study, the authors tested the monoclonal antibody DS6 with 1,202 nongynecologic neoplasms to characterize the full range of expression of antigen CA6. This study has shown that CA6 is highly expressed by many carcinomas of breast, pancreas, and urothelium, and also shows expression in some carcinomas of renal and pulmonary origin, and some neoplasms of other sites. DS6 immunoreactivity is not seen in the majority of neoplasms with hematopoietic, mesenchymal, or germ cell differentiation.