mesothelioma of the pleura

Mesothelioma, even of the pleura alone, is a ubiquitous pathological designation. The diffuse variety is associated with an ominous prognosis. The localized mesothelioma generally has been assumed to be benign. A review of tumors from 60 patients with localized pleural mesothelioma seems to justify separation into benign (52 patients) and malignant (eight patients) variants. Histologic criteria are used primarily to make this division. No single clinical feature allowed preoperative predictability concerning benignity or malignancy, although extrathoracic osteoarthropathy was seen only with benign lesions (20 percent), usually those greater than 7 em. Follow-up periods of as long as 24 years revealed recurrent tumor in only two of the 58 patients with benign lesions and revealed a survival curve identical to that of the general population. All of the patients with the malignant variety had recurrence or metastasis, and all but one were dead within 2 years of the initial operation. One patient died of tumor complications after 9 years. More aggressive local resection is indicated for the malignant variant. Nsidinanya Okike, M.D., Philip E. Bernatz, M.D., and Lewis B. Woolner, M.D., Rochester, Minn. Localized mesothelioma of the pleura was first described by Wagner! in 1870. In 1931, Klemperer and Rabin" distinguished the diffuse from the localized form. Using Maximow's" tissue culture technique, Stout and Murray" in 1942 identified the mesothelial cells as being the origin of this rare pleural tumor. Localized pleural mesothelioma is rare, the incidence being only 2.8 cases per 100,000 registrations at our institution. In contrast to the diffuse pleural mesothelioma, which is always malignant, the localized form generally has been considered to be benign. In our experience, this has not always been true. Patients and methods At the Mayo Clinic, 84 patients have been treated for localized pleural mesothelioma. Twenty-four of these patients were excluded from the study because they were treated before 1950 and their cases have been previously published." From 1950 until December, 1974, surgical resections of localized pleural mesothelioma were carried out in 60 patients, and these From the Mayo Clinic and Mayo Foundation, Rochester, Minn. 55901. Read at the Third Annual Meeting of The Samson Thoracic Surgical Society, Colorado Springs, Colorado, June 4-7, 1977. Address for reprints: Dr. N. Okike, c/o Section of Publications, Mayo Clinic, 200 First Street, S. W., Rochester, Minn. 55901. 0022-5223/78/0375-0363$01.00/0 © 1978 The C. V. Mosby Co. specimens were available for study. Fifty-two of the patients had the benign variant, and eight patients had the malignant variant, as judged histologically. Follow-up information was based on repeated examination of the patient and communication with the patient, the physician, or both. Gross pathological and histologic features Histologically, the localized pleural mesotheliomas were classified into the benign and malignant variants. Benign variant. The localized benign mesothelioma generally is a firm, encapsulated, but lobulated tumor (Fig. I). On cut section, it frequently exhibits a fibrous whorled appearance with occasional calcification, hemorrhage, and central necrosis. Histologically, it is characterized by uniform elongated spindle cells and varied amounts of collagen and reticulum fibers in bundles of many sizes (Fig. 2). The spindle cell contains an oval, slightly indented nucleus with slightly acidophilic cytoplasm. Numerous blood vessels without definite pattern are present. Occasional mitotic figures are seen in cellular zones of a given tumor, but pleomorphism and nuclear anaplasia are absent. Depending on the area sampled, three histologic patterns can be distinguished: fibrous or acellular (Fig. 2, A,), cellular (Fig. 2, B), and mixed (Fig. 2, C). In our series, we avoided classification into these three sub-