Malignant epithelial mesothelioma of the peritoneum: observations on a problem case

Extrathoracic Mesothelial Proliferations and Their Mimics

Mesothelial proliferations, either reactive or neoplastic in nature, often pose difficult diagnostic dilemmas. Electron microscopy continues to be a gold standard in the identification of mesothelial differentiation. However, it is very common to apply long panels of antibodies for that purpose. In most cases, light microscopy and immunohistochemistry will solve the problem. However, the definitive, specific, and sensitive immunohistochemical marker is still lacking. This is particularly true in peritoneal and testicular mesothelial tumors, in which common embryologic origin with epithelial elements results in overlapping immunohistochemistry and morphology. The particularities of peritoneal and testicular mesothelial proliferations, and the main tumors that may mimic them in these sites, as well as the value and limitations of immunohistochemistry and electron microscopy in their differential diagnosis are the subject of this review.

Basal lamina reduplication in malignant epithelioid pleural mesothelioma

Malignant mesothelioma of the pleura is divided in three morphological variants: epithelioid, sarcomatous, and biphasic. Histological similarities between epithelioid malignant mesothelioma (EMM) and lung adenocarcinoma are responsible for the difficult differential diagnosis. Monoclonal antibodies are useful for distinguishing the two neoplasms through immunohistochemical phenotyping, although many cases require ultrastructural characterization for definitive diagnosis. In this study, transmission electron microscopic observations of EMM were compared with those of peripheral adenocarcinoma of the lung (PAL). More specifically, the morphology of the basal lamina is described in 23 cases of EMM and 12 cases of PAL. Reduplication of the basal lamina (RBL) was found in 11 cases (48%) of EMM and in none of the PAL cases. The same cases were immunostained for type IV collagen and the localization of this basement membrane component corresponded to the areas where basal lamina was observed. Since RBL has been associated with neoplastic differentiation in other tumors, this novel feature in EMM needs to be evaluated in future prognostic studies in malignant mesothelioma of the pleura. Moreover, RBL expression in EMM may be an additional ultrastructural parameter used in the differential diagnosis between EMM and adenocarcinoma.

Papillary serous carcinoma of the peritoneum in a man: a case report

BACKGROUND

Papillary serous carcinoma of the peritoneum (PSCP) is a rare primary peritoneal tumor, described exclusively in women. It is believed to arise from the secondary müllerian system, which is comprised of the pelvic and lower abdominal mesothelial lining and subjacent (subcoelomic) mesenchyme in women. Both mesotheliomas and PSCP arise from the coelomic epithelium, but are clinicopathologically and biologically distinct entities.

METHODS

The authors report clinicopathologic findings in a man, age 74 years, who died 3 months after the diagnosis of an extensive malignant abdominal disease.

RESULTS

The routine histologic and immunocytochemical studies of tumor tissue, obtained during the patient's lifetime and at autopsy, validated the unique occurrence of PSCP in a man.

CONCLUSIONS

This case illustrates that PSCP can occur in a man and that this diagnosis may be considered in the differential diagnosis of papillary serous tumors of the peritoneum in male patients. Although rare, PSCP is a diagnostically distinct entity the treatment of which is similar to ovarian serous tumors rather than mesotheliomas.