Localized malignant mesothelioma, an unusual and poorly characterized neoplasm of serosal origin: best current evidence from the literature and the International Mesothelioma Panel

Our plain-English summary of Localized malignant mesothelioma, an unusual and poorly characterized neoplasm of serosal origin: best current evidence from the literature and the International Mesothelioma Panel, by A.M. Marchevsky, A. Khoor, A.E. Walts, et al (Modern Pathology, 2020).

The study

• Authors: A.M. Marchevsky, A. Khoor, A.E. Walts, A.G. Nicholson, Y.Z. Zhang, V. Roggli, J. Carney, A.C. Roden, H.D. Tazelaar, B.T. Larsen, N. LeStang, L.R. Chirieac, S. Klebe, M.S. Tsao, M. De Perrot, A. Pierre, D.M. Hwang, Y.P. Hung, M. Mino-Kenudson, W. Travis, J. Sauter, M.B. Beasley, F. Galateau-Sallé
• Journal: Modern Pathology
• Published: 2020;33(2):281-296
• Type of article: Review
• Cited by: 42 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Localized malignant mesotheliomas (LMM) is an uncommon and poorly recognized neoplasm. Its pathologic diagnosis is often surprising in patients with serosal/subserosal based localized tumors that are clinically suspicious for metastatic lesions or primary sarcomas. Once a tumor is diagnosed as "mesothelioma", LMM is often mistaken for diffuse malignant mesothelioma (DMM). Best currently available evidence about LMM was collected from the literature and cases diagnosed by members of the International Mesothelioma Panel (IMP). One hundred and one (101) LMM have been reported in the English literature. Patients had localized tumors with identical histopathologic features to DMM. Patients ranged in age from 6 to 82 years; 75% were men. Most (82%) of the tumors were intrathoracic. Others presented as intrahepatic, mesenteric, gastric, pancreatic, umbilical, splenic, and abdominal wall lesions. Tumors varied in size from 0.6 to 15 cm. Most patients underwent surgical resection and/or chemotherapy or radiation therapy. Median survival in a subset of patients was 29 months. Seventy two additional LMM from IMP institutions ranged in age from 28 to 95 years; 58.3% were men. Sixty tumors (83.3%) were intrathoracic, others presented in intraabdominal sites. Tumors varied in size from 1.2 to 19 cm. Median survival for 51 cases was 134 months. Best evidence was used to formulate guidelines for the diagnosis of LMM. It is important to distinguish LMM from DMM as their treatment and prognosis is different. A multidisciplinary approach is needed for the diagnosis of LMM as it shows identical histopathology and immunophenotype to DMM.

In plain English

This article combined a literature review with a new case series on localized malignant mesothelioma (LMM). LMM is a localized tumor that looks identical under the microscope to diffuse malignant mesothelioma (DMM), though published studies defined "localized" differently. The review found 101 published cases. Of these, 75% were men; 29 of 78 with exposure information (37.2%) had asbestos exposure, of undescribed type and length. Members of the International Mesothelioma Panel at 12 institutions contributed 72 previously unreported cases. Among 38 of these patients with exposure information, 21 (55.2%) had asbestos exposure noted. Pleural plaques were reported in seven patients. The one case with tissue fiber analysis showed tremolite fibers at background levels. Among 51 panel patients surviving at least one month, median survival was 134 months (95% CI 65 to 134 months), shorter for sarcomatoid and biphasic than epithelioid tumors; the authors urged caution because treatment and follow-up varied. The authors concluded that LMM patients have considerably more favorable survival than DMM patients, and that evidence is insufficient to determine whether asbestos exposure increases LMM risk. They proposed diagnostic guidelines.

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: Review of published English-language case reports and case series, plus a retrospective multi-institution case series contributed by International Mesothelioma Panel members, used to propose opinion-based diagnostic guidelines
• Who was studied: 101 LMM cases described in 51 publications from 1978 to 2019, and 72 previously unreported LMM cases from 12 institutions in the United States, the United Kingdom, France, Australia and Canada
• Exposure: Asbestos exposure as noted in clinical or occupational histories. Examples included household exposure, shipyard and U.S. Navy work, and other jobs listed in the case table. Fiber type and dose were mostly not reported.
• Main results:
  • Literature cases: patients had localized tumors with microscopic features identical to DMM.
  • Published LMM cases used various interpretations of the criteria for calling a mesothelioma localized. Some included small nodules next to the main tumor, limited pleural thickening, or pleural effusion.
  • Literature cases: 76 of 101 were men (75%). Of 78 patients with exposure information, 29 (37.2%) had asbestos exposure, but the type and length of exposure were not described.
  • Literature cases: a previous pooled analysis of 16 studies by Gelvez-Zapata et al., cited in the review, gave a median survival of 29 months.
  • At two panel institutions (Royal Brompton and Harefield; Cedars-Sinai), LMM made up an estimated 1.6% and 0.5% of all mesothelioma cases diagnosed.
  • Panel cases: 42 of 72 patients were men (58.3%), and 63 tumors (87.5%) were intrathoracic.
  • Panel cases: pleural plaques were reported in seven patients. Asbestos bodies in lung tissue were reported in two patients. In the one case with tissue burden analysis, tremolite fibers were at background levels.
  • Panel cases: the survival analysis included only patients who survived at least one month after diagnosis. Two patients died within one month, which left 51 cases.
  • Panel cases: median survival for 51 patients was 134 months (95% CI 65 to 134 months).
  • Panel cases: median survival was 134 months for epithelioid, 65 months for sarcomatoid and 30 months for biphasic tumors. The survival curves were significantly different (p = 0.039).
  • Panel cases: recurrences were reported in 14 of 51 patients (27.4%).
• The authors' conclusion: The authors concluded that patients with LMM have considerably more favorable survival than patients with DMM, and that the two should be distinguished because treatment and prognosis differ.
• Limitations the authors state:
  • The contributed case data were incomplete for some cases.
  • The survival analysis should be interpreted with caution, because patients were treated differently at multiple institutions and followed for different lengths of time.
  • There is insufficient evidence to determine whether asbestos exposure increases LMM risk, because exposure information is scant and epidemiologic studies are lacking.
  • Published survival data were hard to evaluate because the studies used different diagnostic criteria and treatments.
  • Applying the proposed criteria retrospectively would reclassify some cases diagnosed as LMM as DMM.

Topics

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

Medical terms in this study, explained in our Lexicon: Localized Malignant Mesothelioma, Neoplasm, Mesothelioma, Sarcoma, Malignant Mesothelioma, Intrathoracic, Surgical Resection, Chemotherapy.

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