Pseudomesotheliomatous Carcinoma of the Lung: A Variant of Peripheral Lung Cancer

Abstract

Six cases of primary lung cancer that closely mimic malignant pleural mesothelioma clinically and anatomically are compared with four proven cases of malignant pleural mesothelioma. Findings on roentgenograms of the chest, clinical history, and gross examination of the lung specimens are not helpful in distinguishing between these two neoplasms. Microscopic examination of the hematoxylin and eosin-stained tissues is often inconclusive. Tissues were stained with hematoxylin and eosin, PAS with and without diastase treatment (DPAS), mucicarmine, alcian blue, toluidine blue, and colloidal iron with and without digestion by testicular hyaluronidase. Among these histochemical methods, DPAS was found to be particularly useful in distinguishing the primary lung cancers from the mesotheliomas. All primary lung cancers except one showed DPAS-positive material (mucin) in both the cytoplasm of the cancer cells and within the lumina of neoplastic glands. In contrast, none of the mesotheliomas showed the presence of DPAS-positive material. Histologically, all lung cancers were glandular. Five were classified as bronchiolar carcinoma, the remaining one as poorly differentiated adenocarcinoma. In two of the bronchiolar carcinomas, a small subpleural primary focus was demonstrated. This finding suggests a possible origin of these cancers as a small subpleural tumor that became widely disseminated via the subpleural lymphatics. This form of primary lung cancer possesses sufficient gross and microscopic characteristics that recognition should be given to it as a variant of primary lung cancer, with emphasis on differentiating it from pleural mesothelioma.

Mucin-negative Pseudomesotheliomatous Adenocarcinoma of the Lung: Report of Three Cases

“…Mucin was identified in all 6 cases described by Harwood et al (4). In all 12 PMAL cases previously reported (4, 8 -11), epithelial mucin was demonstrated in the neoplastic cells.…”

“…The average survival of 12 PMAL cases previously reported (4,(8)(9)(10)(11)) was 6 months after admission. Koss et al (12) reported that all PMAL patients dies with/of tumor, with a mean survival of 4.7 months for those reported in the medical literature and of 7 months for those in the Armed Forces Institute of Pathology files.…”

“…If no or few mucins are demonstrated, a further diagnostic approach is needed to rule out non-mucin-producing adenocarcinoma of the lung (3). Harwood et al (4) coined the term pseudomesotheliomatous adenocarcinoma of the lung (PMAL) to identify a distinct variant of peripheral lung cancer characterized by extensive pleural growth with slight parenchymal involvement. The tumor is clinically, radiologically, macroscopically, and morphologically indistinguishable from malignant pleural mesothelioma.…”

Cytologic Presentation of Malignant Mesothelioma in Pleural Effusions

“…(2) The malignant meso thelioma mimics other carcinomas from small cell carcinomas to adenocarcinomas metastasizing to the pleura [2][3][4][5], However, malignant cells in pleural effu sions due to carcinomatous mesothelioma may show typical morphologic features. They consist of multinucleation, optically dense cytoplasm with changing staining be havior, marginal vacuolisation, 'windows' between two adjacent cells and 'cell in cell' formation of malignant cells.…”

Histopathology of the Pleura

“…Adenocarcinoma is seen most frequently, and primary sites include lung, breast, gastrointestinal tract, ovary, thyroid and kid ney [142], In many cases, the primary site is not deter mined during life [143,144], Some peripheral adeno carcinomas of the lung, and more rarely squamous carcinomas, spread over pleural surfaces in a manner similar to mesothelioma and it may be difficult to es tablish where in the lung such tumours have origi nated [145]. In distinguishing between secondary adenocarcinoma of the pleura and mesothelioma of epithelial type, mucus stains, immunohistochemistry and electron microscopy are all helpful (see above).…”