The Fake Fat Phenomenon in Organizing Pleuritis: A Source of Confusion With Desmoplastic Malignant Mesotheliomas
We report 9 patients with pleural biopsies referred because of concern about infiltration of what appeared to be chest wall fat by pan-keratin-positive spindled cells, a finding that led to a consideration of desmoplastic mesothelioma. All patients showed pleural effusions/pleural thickening on computed tomographic scan. Pleural biopsy showed a greatly thickened and fibrotic paucicellular pleura with circular fat-like spaces and, sometimes, adjacent oblate spaces mostly deep in the fibrotic area. Indistinct, keratin-positive, spindle cells arranged parallel to the pleural surface coursed between these fat-like spaces. S-100 stains were negative around the fat-like spaces. Vimentin stains showed that the spaces did not have a cellular lining of any kind. Sometimes the spaces contained faintly hematoxyphilic material that was Alcian blue positive, and similar material was seen in the fibrotic stroma. Follow-up with periods ranging from 6 to 30 months revealed that 8 cases had stable disease on chest imaging or by clinical findings. One case had slowly progressive pleural thickening. These observations suggest that spaces resembling fat may be encountered in fibrotic pleurae and that horizontally oriented keratin-positive spindled cells between the fat-like spaces deep in the fibrotic portion of a thickened pleura represent a benign finding seen in some cases of organizing pleuritis/fibrothorax. The spaces themselves are probably artifacts derived from the biopsy procedure and/or cutting artifacts. In contrast, in true desmoplastic mesotheliomas there is downward, rather than horizontal, growth of keratin-positive spindled cells running between clearly definable fat cells.
Available from: Sergio Piña-Oviedo
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ABSTRACT: Diffuse malignant mesothelioma (DMM) is an uncommon cancer with great clinical significance because it currently remains an incurable disease, and most patients die within months after diagnosis. Although DMM incidence is leveling off or decreasing in developed countries because of the strict control of asbestos use, it is increasing in countries without adequate asbestos control. In some settings, benign, reactive mesothelial hyperplasias and organizing pleuritis can be difficult to differentiate from DMM and vice versa, and the variety of DMM's histopathologic features generates an extensive list of differential diagnoses with other malignancies, particularly, metastatic malignancies, which are more frequent in the pleura than are primary malignancies. These two issues are the topic of discussion in this review, along with a brief presentation of a case of DMM that presented in a 66-year-old man with recurrent, right pleural effusions, and in whom, diagnosis of DMM had not been suspected clinically, radiographically, surgically, grossly, or initially, on frozen section. It was not until focal invasion into the skeletal muscle was discovered on permanent sections that a diagnosis of DMM could be established.
Available from: archivesofpathology.org
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ABSTRACT: The separation of benign from malignant mesothelial proliferations is crucial to patient management but is often a difficult problem for the pathologist.
To review the pathologic features that allow separation of benign from malignant mesothelioma proliferations, with an emphasis on new findings.
Literature review and experience of the authors.
Invasion is still the most reliable indicator of malignancy. The distribution and amount of proliferating mesothelial cells are important in separating benignity from malignancy, and keratin stains can be valuable because they highlight the distribution of mesothelial cells. Hematoxylin-eosin examination remains the gold standard, and the role of immunochemistry is extremely controversial; we believe that at present there is no reliable immunohistochemical marker of malignancy in this setting. Mesothelioma in situ is a diagnosis that currently cannot be accurately made by any type of histologic examination. Desmoplastic mesotheliomas are characterized by downward growth of keratin-positive spindled cells between S100-positive fat cells; some cases of organizing pleuritis can mimic involvement of fat, but these fat-like spaces are really S100-negative artifacts aligned parallel to the pleural surface. Fluorescence in situ hybridization on tissue sections to look for homozygous p16 gene deletions is occasionally useful, but many mesotheliomas do not show homozygous p16 deletions. Equivocal biopsy specimens should be diagnosed as atypical mesothelial hyperplasia and another biopsy requested if the clinicians believe the process is malignant.
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ABSTRACT: This article provides evidence-based background and recommendations for the development of American College of Chest Physicians guidelines for the diagnosis and management of lung cancer. Specific population, intervention, comparison, and outcome questions were addressed to arrive at consensus recommendations.
A systematic search of the medical and scientific literature using MEDLINE and PubMed was performed for the years 1990 to 2011 and limited to literature on humans and articles written in English. Our approach to examining the evidence and formulating recommendations is described in the "Methodology for Lung Cancer Evidence Review and Guideline Development: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (2nd Edition)" and updated in "Methodology for Development of Guidelines for Lung Cancer: Diagnosis and Management of Lung Cancer, 3rd ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines."
Pathologic examination results of lung cancers should be recorded in a synoptic form to include important prognostic features of histologic type, tumor size and location, involvement of visceral pleura, extension to regional and distant lymph nodes, and metastatic spread to visceral organs and bone to increase completeness of recording. It is important for the surgical pathologist to make distinctions between malignant mesothelioma and pleural adenocarcinomas, small cell and non-small cell carcinomas, adenocarcinomas and squamous cell carcinomas, and primary and metastatic carcinomas of the lung. In challenging cases of pathologic differential diagnosis, additional studies may enable the separation of distinct tumor types.
Pathologic assessment of lung cancers is a crucial component for the diagnosis, management, and prognosis of lung cancer, making the pathologist a critical member of the clinical and management team. Selective diagnostic techniques, including limited designed immunohistochemical panels, and decision analysis will increase diagnostic accuracy.
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