Diffuse intrapulmonary malignant mesothelioma masquerading as interstitial lung disease: a distinctive variant of mesothelioma

Our plain-English summary of Diffuse intrapulmonary malignant mesothelioma masquerading as interstitial lung disease: a distinctive variant of mesothelioma, by B.T. Larsen, J.R. Klein, H. Hornychová, et al (The American Journal of Surgical Pathology, 2013).

The study

• Authors: B.T. Larsen, J.R. Klein, H. Hornychová, R. Nuti, S. Thirumala, K.O. Leslie, T.V. Colby, H.D. Tazelaar
• Journal: The American Journal of Surgical Pathology
• Published: 2013;37(10):1555-64
• Type of article: Case report
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant mesothelioma typically encases lungs as a thick rind, while relatively sparing lung parenchyma. We describe an unusual presentation of mesothelioma characterized by diffuse intrapulmonary growth, with absent or inconspicuous pleural involvement, clinically simulating interstitial lung disease (ILD). We identified 5 patients (median age 56 y, all men) with diffuse intrapulmonary malignant mesothelioma in our pathology consultation practice from 2009 to 2012. Clinical history, imaging, and pathology materials were reviewed. Symptoms included chronic dyspnea (4 cases), cough (3), and acute dyspnea with bilateral pneumothorax (1). Chest imaging showed irregular opacities (5), reticulation (4), pleural effusions (2), and subpleural nodular densities (1), without radiologic evidence of pleural disease or masses. A clinicoradiologic diagnosis of ILD was made in all cases, and wedge biopsies were performed. Histologic evaluation revealed a neoplastic proliferation of bland epithelioid or spindled cells, showing various growth patterns simulating silicotic nodules, desquamative interstitial pneumonia, organizing pneumonia, and Langerhans cell histiocytosis. Some areas mimicked adenocarcinoma, with lepidic, acinar, micropapillary, and solid patterns. Initial diagnoses by referring pathologists included reactive changes (1), hypersensitivity pneumonitis versus drug reaction (1), desquamative interstitial pneumonia versus neoplasm (1), and mesothelioma (2). Microscopic pleural involvement was identified in 4 cases. Immunohistochemistry confirmed the characteristic immunophenotype of mesothelioma in all cases. Median survival of 3 patients treated with chemotherapy was 28 months. Two patients received no therapy and survived 3 and 4 weeks, respectively. "Diffuse intrapulmonary malignant mesothelioma" is a rare variant with a distinctive presentation that clinically mimics ILD. Recognition is essential to avoid misdiagnosis.

In plain English

This case series described 5 patients with a rare form of malignant mesothelioma, which the authors called diffuse intrapulmonary malignant mesothelioma. The cases came from about 900 mesothelioma cases (0.6%) seen in the Mayo Clinic pathology consultation practice from 2009 to 2012. All 5 were men, median age 56. Instead of forming the usual thick rind on the pleura, the tumor grew mainly inside the lung, and all 5 were initially thought, from symptoms and imaging, to have interstitial lung disease. Referring pathologists called 2 cases mesothelioma. They read the others as other conditions, such as reactive changes, or hypersensitivity pneumonitis versus drug reaction. Microscopic pleural involvement was found in 4 cases, and stains confirmed mesothelioma in all 5. Asbestos exposure was recorded as yes for 1 patient (details unavailable) and no for 4. No asbestos bodies were found in any case. Three patients given chemotherapy survived 21 months, 44 months, and 28 months (still alive). Two untreated patients survived 3 and 4 weeks. The authors could not tell whether the longer survival reflected chemotherapy or smaller tumor burden. They concluded that recognizing this variant is essential to avoid misdiagnosis.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case series (retrospective review of pathology consultation cases), with comparison to previously reported cases
• Who was studied: 5 patients, all men (ages 53, 70, 55, 56 and 81; median 56), identified among approximately 900 malignant mesothelioma cases in the Mayo Clinic pathology consultation practice, 2009 to 2012
• Exposure: History of asbestos exposure was recorded as 'No' for cases 1 to 4 and 'Yes (details unavailable)' for case 5. No fiber types were reported for this series. Asbestos bodies were not found in any case's tissue. Four patients had a smoking history; it was unknown for case 5.
• Main results:
  • 5 of approximately 900 malignant mesothelioma cases (0.6%) in the consultation practice presented as interstitial lung disease
  • In all 5 cases, the presumptive clinical and imaging diagnosis was interstitial lung disease, and wedge biopsies were done for histologic diagnosis
  • Referring pathologists' initial diagnoses were reactive changes (1), hypersensitivity pneumonitis versus drug reaction (1), desquamative interstitial pneumonia versus neoplasm (1), and mesothelioma (2)
  • Focal microscopic pleural involvement was found in 4 of the 5 cases, without pleural thickening. A small pleural plaque was seen in 1 case.
  • 3 cases were biphasic and 2 were epithelioid type. No case was purely sarcomatoid or desmoplastic.
  • Asbestos bodies were not found in any of the 5 cases
  • In each case, at least 3 mesothelial markers were positive and at least 3 carcinoma markers were negative, consistent with mesothelioma
  • Median survival of the 3 chemotherapy-treated patients was 28 months. Individually: 28 months and still alive with disease (case 1), died at 44 months (case 2), died at 21 months (case 4).
  • The 2 patients who received no therapy survived 3 and 4 weeks
• The authors' conclusion: The authors concluded that this rare variant is associated with a poor prognosis, as with classical mesothelioma. They found that at least some patients appear to respond to chemotherapy, and that recognizing the variant is essential to avoid misdiagnosis.
• Limitations the authors state:
  • The cases came from a referral practice, so the actual incidence may be below 0.6%
  • It is unclear whether the longer survival in the 3 treated patients was due to chemotherapy or to lesser tumor burden at diagnosis

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Interstitial Lung Disease, Mesothelioma, Parenchyma, Pathology, Dyspnea, Bilateral, Pneumothorax.

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• Asbestosis: demonstration of distinctive interstitial fibroelastosis: a pilot study — M.R. Wick, T.J. Kendall, et al. (2009)
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