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Fifty-seven cases of mesothelioma from the Toronto General Hospital during the period 1965 to 1976 have been reviewed. Pleural effusions or ascites were present in 34 patients. The value of cytologic examination of effusion specimens was assessed, and the criteria for cytologic diagnosis were elucidated. It appears that patients with predominantly fibrous or sarcomatous mesothelioma were not prone to develop pleural effusions or ascites; few tumor cells, if any, from these mesotheliomas were exfoliated into effusions. Cytologic examinations of effusion specimens were positive in 12 of 14 cases of carcinomatous mesothelioma and in three of four cases of undifferentiated mesothelioma. However, only four of seven casee of benign mesothelioma (mostly epithelial type) showed positive results, as did two of four cases of sarcomatous mesothelioma. It appears that cytologic diagnosis of mesothelioma is more useful for the carcinomatous and undifferentiated types. The cytomorphologic features of the various types of mesothelioma are different, and by cytologic examination of effusion specimens, typing of mesothelioma is possible and correlates well with the histologic typing.

A distinction is drawn between first category includes peduncolates, giant seslocal and diffuse primary tumours of the pleura on anatomopathological grounds. The first category includes peduncolated, giant sessile, and "deceptive" forms; the latter those in which the lung is surrounded by a "pleural" and "serous" mantle. Treatment is discussed and the soundness of surgical management is stressed.

Of 394 "definite" mesotheliomas entered in the Australian Mesothelioma Surveillance Program, three bore a striking resemblance to malignant lymphoma by conventional light microscopy, and each was misinterpreted at some stage as lymphoma. The lymphoma-like morphology was a combined result of intense lymphoplasmacytic infiltration and the histiocytoid appearances of the underlying neoplastic cell population. Immunocytochemical analysis demonstrated cytokeratins coexpressed with vimentin within the tumor cells, whereas immunoreactivity for leukocyte common antigen was confined to the smaller lymphoid cells. Electron microscopy of two cases revealed a polymorphous population of fibrohistiocytic cells resembling those typical of malignant fibrous histiocytoma, admixed with lymphocytes and plasma cells, but sporadic cells expressed mesothelial properties in the form of sinuous villiform processes, intracytoplasmic neolumina lined by microvilli, and intermediate filaments that were aggregated into tonofilament bundles in some cells. The ultrastructural appearances, the localization of the tumors to the pleura, with effusion, and absence of anterior mediastinal mass lesions facilitated exclusion of lymphocyte-rich thymoma. In addition, a history of prior occupational exposure to asbestos was elicited in each instance. There was no apparent response to radiotherapy or chemotherapy, and the patients died at 4, 5, and 8 months after presentation. Our observations suggest that immunocytochemical or ultrastructural evaluation is mandatory for accurate diagnosis of all pleura-based lymphomatoid lesions with a mixed large and small cell pattern.

Of 21 primary peritoneal, omental, and mesenteric tumors, 14 were cysts and seven were solid. Most of the cysts were omental-mesenteric lymphangiomas; the sole exception was a cystic mesothelioma in a newborn. The solid tumors included three multicentric hamartomas, three sarcomas of undetermined histogenesis, and one immature teratoma. Since cystic lymphangiomas carry a good prognosis following surgical excision, they must be distinguished from cysts of mesothelial origin. Solid hamartomas may simulate malignant tumors because of multicentricity and immature tissue composition. Although peritoneal sarcomas of undetermined histogenesis are apt to be large, composed of primitive cells, and disposed to the development of implants, current treatment modalities may control the disease. One of three treated patients survived for 8 years. A child with a solid immature teratoma without a malignant germ-cell component remains free of disease 5 years after diagnosis. Our review, which represents the combined experience of two children's hospitals over several decades, did not include tumors such as malignant mesothelioma, lipoma, liposarcoma, leiomyoma, mesenchymoma, fibromatosis, and other neoplasms, which may rarely arise in the peritoneum, omentum, and mesentery of children.

Ninety-six primary cardiac neoplasms were identified from 79,971 Fischer 344 (F344) rats used in chronic toxicity and carcinogenicity studies by the National Toxicology Program (NTP) and National Cancer Institute (NCI), for an overall incidence of 0.1%. Neoplasms were classified as: 60 endocardial schwannomas, 23 intramural schwannomas, eight atriocaval mesotheliomas, three paragangliomas, one pericardial mesothelioma, and one hemangioma. Metastases occurred in four rats with endocardial schwannoma. Histological appearance of the endocardial and intramural schwannomas was consistent with origin from nerve sheath. Two of six endocardial schwannomas available for immunohistochemical staining were weakly positive for S-100 antigen. The atriocaval mesotheliomas, while morphologically resembling adenocarcinoma, were positive for vimentin and keratin, indicating mesothelial origin. Seventy of the 96 cardiac neoplasms occurred in rats 2 years of age or older at time of death. There were no sex or treatment-related differences in the incidence of these neoplasms, with the exception of atriocaval mesothelioma, which was more common in males.

Eight cases of adenomatoid tumors of the male genital tract are presented. Histological, histochemical, and electron microscopic studies were performed and an approach to a new classification of adenomatoid tumors was discussed. The number of so-called adenomatoid tumors of male genital tract reported in Japan adding our eight cases totalled 60 cases. These were classified as follows; 10 cases of mesothelial (superficial) type and 50 cases of adenomatoid (profound) type. Besides these, 8 cases of mesothelial type were reported in foreign literatures. Three cases of adenomatoid tumors of the uterus and a case of epididymitis chronica with reactive proliferation of mesothelial cells were also examined. As a result of these investigations, it is suggested that the histogenesis of the so-called adenomatoid tumors is composed of two different processes; i.e., mesothelial type arising from serosal mesothelial cells. and adenomatoid type arising from immature Müllerian mesenchymal tissue.

An investigation into the effect of national death certification and coding practices on published mortality statistics in eight EEC countries is reported. Doctors in each country were asked to complete specimen death certificates for a bank of written case histories. Certificates from each country were coded by their own offices and then by a WHO reference centre. Within and between countries, discrepancies occurred both in the doctors' diagnoses and in the codes assigned to certificates. At an international level these differences had serious implications for the comparability of mortality data for cancers of the cervix and uterus, and for mesotheliomas.