From Ascites to Malignant Peritoneal Mesothelioma: The Diagnostic Workup of a Rare Tumor

Our plain-English summary of From Ascites to Malignant Peritoneal Mesothelioma: The Diagnostic Workup of a Rare Tumor, by M. Nastasi, C. Ferrante, G. Michelis, et al (Cancer Diagnosis & Prognosis, 2026).

The study

• Authors: M. Nastasi, C. Ferrante, G. Michelis, E. Branca, M. Ventura, S. Novello, E. Laurita
• Journal: Cancer Diagnosis & Prognosis
• Published: 2026;6(4):803-809
• Read it: PubMed · Publisher · Free full text

Abstract

Background/aim: Ascites is a common clinical manifestation of a wide spectrum of heterogeneous underlying conditions. All possible causes of ascites should be considered in the differential diagnosis to ensure an appropriate diagnostic workup. Among the rare causes, malignant peritoneal mesothelioma must be considered, as its diagnosis is particularly challenging.

Case Report: We present the case of a 77-year-old female who developed ascites and lower-quadrant abdominal pain. She had no prior history of cancer and no documented occupational exposure to asbestos or other known carcinogens. After exclusion of the principal benign and malignant causes of ascites, we performed a biopsy and 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). The final diagnosis was primary malignant peritoneal mesothelioma, an extremely rare tumor.

Conclusion: This case highlights the complexity of the differential diagnosis. The diagnostic work-up for peritoneal mesothelioma must integrate the patient's clinical history, physical examination, tumor markers, and imaging findings. Biomarkers such as mesothelin and advanced imaging modalities including PET/CT assume an increasingly important role in staging and in distinguishing peritoneal disease entities.

©2026 The Author(s). Published by the International Institute of Anticancer Research.

In plain English

This article is a case report about one 77-year-old woman admitted to Rivoli Hospital near Turin, Italy, with repeated vomiting and diarrhea and pain in the lower abdomen. Fluid had built up in her abdomen (ascites), and eight liters were drained. The fluid results were consistent with a cause other than portal hypertension; cytology (a test for cancer cells) and cultures were negative. Of the tumor markers tested, only CA-125 was raised, at 164 UI/ml. A CT scan showed thickening of the abdominal lining and a 40 mm mass in the pelvis. A first needle biopsy suggested malignant peritoneal mesothelioma but had too few cells for full testing. A PET/CT scan showed no significant metabolic activity in the abdomen. A second biopsy confirmed the epithelioid subtype of peritoneal mesothelioma, and the diagnosis took over five weeks in total. No occupational exposure, including asbestos, was identified, although the authors wrote that indirect exposure could not be ruled out. The authors concluded that this tumor remains difficult to diagnose because it is rare, its symptoms are non-specific, and many other causes must be excluded.

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 (single patient)
• Who was studied: One 77-year-old woman admitted to the Internal Medicine ward of Rivoli Hospital (Turin, Italy); dates of care not given
• Exposure: No specific occupational exposure, including asbestos, was identified; the authors note indirect exposure cannot be ruled out. No fiber type or dose is reported.
• Main results:
  • Paracentesis drained eight liters of fluid from the patient's abdomen; the results were consistent with an exudate not caused by portal hypertension (SAAG 0.74)
  • Microbiological cultures and cytology of the patient's ascitic fluid were negative
  • Of the tumor markers measured in this patient, only CA-125 was elevated, at 164 UI/ml (cut-off 0-35 UI/ml)
  • Contrast-enhanced CT showed peritoneal thickening and a 40 mm solid mass in the pararectal region of the pelvis
  • The first fine-needle biopsy suggested malignant peritoneal mesothelioma but had too few cells for full immunohistochemical analysis
  • FDG-PET/CT showed no significant metabolic activity in the abdominal tissue
  • A second biopsy confirmed the epithelioid subtype of peritoneal mesothelioma
  • Reaching a definitive diagnosis took over five weeks
• The authors' conclusion: The authors concluded that diagnosing malignant peritoneal mesothelioma remains difficult because of its rarity, non-specific presentation and complex differential diagnosis, and that the absence of a clear exposure history made this case particularly challenging

Topics

Medical terms in this study, explained in our Lexicon: Ascites, Peritoneal Mesothelioma, Differential Diagnosis, Occupational Exposure, Biopsy, Tumor Marker, Biomarker, Mesothelin.

Related studies

• Malignant Peritoneal Mesothelioma as a Rare Cause of Dyspeptic Complaints and Ascites: A Diagnostic Challenge — S. Marques de Sousa, F. Pereira, et al. (2020)
• Biphasic Peritoneal Mesothelioma Is a Rare Tumor and a Diagnostic Challenge: A Case Report — E.A. Subahi, A. Fadul, et al. (2024)
• Malignant peritoneal mesothelioma as a rare cause of ascites: a case report — I. Ahmed, A. Koulaouzidis, et al. (2008)
• Malignant Peritoneal Mesothelioma: A Rare Cause of Ascites — A.M. Ibrahim, M. Al-Akchar, et al. (2018)
• Ascites as a Rare Manifestation of Malignant Peritoneal Mesothelioma: A Case Report — S. Lief, S. Patibandla, et al. (2024)
• A Rare Case of Biphasic Malignant Peritoneal Mesothelioma with Refractory Ascites — T. Komaki, H. Urata, et al. (2017)

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