Pseudocarcinomatous Mesothelioma: A Hitherto Unreported Presentation closely simulating primary lung cancer

Our plain-English summary of Pseudocarcinomatous Mesothelioma: A Hitherto Unreported Presentation closely simulating primary lung cancer, by G. Rossi, G. Caroli, D. Caruso, et al (International Journal of Surgical Pathology, 2021).

The study

• Authors: G. Rossi, G. Caroli, D. Caruso, F. Stella, F. Davoli
• Journal: International Journal of Surgical Pathology
• Published: 2021;29(7):775-779
• Type of article: Review
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant mesothelioma (MM) has a wide range of clinical, radiologic, and pathologic presentations, mimicking lung cancer or interstitial lung diseases when predominantly involving the lung parenchyma. The case herein refers to a 79-year-old man, active smoker without asbestos exposure, incidentally discovered to have a pulmonary nodule in the right upper lobe (1.5 cm). The lesion was misinterpreted as primary lung adenocarcinoma at the frozen section in light of the predominant lepidic growth pattern. Definitive examination confirmed neoplastic proliferation along alveolar structures. However, the unusual globous shape of tumor cells along the alveoli abruptly merging with normal pneumocytes prompted us to perform some immunostains that surprisingly revealed a mesothelial differentiation (positive staining with calretinin, cytokeratins (CK5/6), D2-40, and negativity with BRCA-associated protein 1 (BAP1), Thyroid Transcription Factor 1 [TTF-1], claudin-4, carcinoembryonic antigen [CEA], and napsin). MM represents the pathologic counterpart of so-called pseudomesotheliomatous carcinoma, since it appears as a localized pulmonary neoplastic nodule displaying a predominant lepidic growth pattern (pseudocarcinomatous mesothelioma). The challenging diagnostic features of this unique case and a review of similar cases in the literature are discussed.

In plain English

This was a case report from a hospital in Ravenna, Italy, about one 79-year-old man. He was an active smoker (25 packs/year) and had no reported history of asbestos exposure. After he was treated for pneumonia, a CT scan showed a small 15 mm nodule in the upper lobe of his right lung. Several needle biopsies gave no diagnosis, so surgeons removed the nodule. During the operation, a rapid frozen-section test wrongly identified it as lung adenocarcinoma, because the tumor cells grew along the lung's air sacs (a 'lepidic' pattern), which made up about 80% of the nodule. Later staining tests showed mesothelial features, and the final diagnosis was malignant mesothelioma, epithelioid variant, growing inside the lung. After surgery the patient had an air leak and a collapse of the right lung, was treated with talc pleurodesis, and was on cancer follow-up. The authors called this a previously unreported presentation. They concluded that a wider panel of markers than usual seems necessary to recognize it. A single case shows what happened to one person, not how often this occurs.

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 report of a single patient, with discussion of similar cases previously reported in the literature
• Who was studied: One 79-year-old white man, an active smoker with chronic obstructive pulmonary disease (COPD), treated at Santa Maria delle Croci Hospital, Ravenna, Italy
• Exposure: No history of asbestos exposure was reported. The patient was an active smoker (25 packs/year).
• Main results:
  • CT of the chest showed a small subpleural nodule (15 mm) in the right upper lobe.
  • PET-CT showed uptake in the upper lobe nodule (SUVmax 11.2). Multiple CT-guided needle biopsies gave no diagnosis.
  • On intraoperative frozen sections, the lepidic tumor growth was wrongly interpreted as primary lung adenocarcinoma.
  • On final examination, about 80% of the nodule showed tumor cells growing along the alveolar structures (lepidic pattern).
  • Immunostains were strongly and diffusely positive for pan-cytokeratins, cytokeratins 5/6, calretinin and podoplanin (D2-40). They were negative for TTF-1, CDX2, napsin, claudin-4 and CEA, and also negative for BAP1.
  • The final diagnosis was malignant mesothelioma, epithelioid variant, with intrapulmonary and predominantly lepidic growth.
  • After surgery there was a persistent air leak. The patient was readmitted on postoperative day 33 with severe dyspnea and a severe collapse of the right lung, and was treated with talc pleurodesis. At the time of reporting, the patient was on oncological follow-up.
• The authors' conclusion: The authors concluded that this solitary lung nodule with predominant lepidic growth was a hitherto unreported presentation of malignant mesothelioma that simulated primary lung cancer, including on frozen section. In their view, a larger panel of mesothelial and nonmesothelial markers than is used in conventional mesothelioma seems mandatory to recognize it.

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: Mesothelioma, Lung Cancer, Malignant Mesothelioma, Interstitial Lung Disease, Parenchyma, Asbestos Exposure, Lung Adenocarcinoma, Frozen Section.

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