Localized Epithelioid Peritoneal Mesothelioma: A Rare Mimicker of Gynecological Malignancy

Our plain-English summary of Localized Epithelioid Peritoneal Mesothelioma: A Rare Mimicker of Gynecological Malignancy, by F. Carvalho, D. Pereira, T.M. Cunha (Curēus, 2026).

The study

• Authors: F. Carvalho, D. Pereira, T.M. Cunha
• Journal: Curēus
• Published: 2026;18(7):e112299
• Type of article: Case report
• Read it: PubMed · Publisher · Free full text

Abstract

Localized epithelioid peritoneal mesothelioma (LEPM) is a rare variant of peritoneal mesothelioma that presents as a solitary, circumscribed mass rather than with the diffuse serosal spread that characterizes the far more common diffuse form. Because it may arise in the pelvis and be accompanied by ascites and a mildly elevated carbohydrate antigen (CA)-125 level, it is readily mistaken for a gynecological or primary peritoneal malignancy. Although it is generally regarded as less aggressive than the diffuse form, its clinical behavior can be unpredictable. We report the case of a 76-year-old woman in whom a 5 cm pelvic mass was detected incidentally on transvaginal ultrasound and was initially suspected to be a gynecological malignancy. Preoperative MRI demonstrated clear cleavage planes between the mass and the uterus and left ovary, indicating a non-gynecological origin, and surgery confirmed the presence of a tumor on the antimesenteric border of the small bowel. Histopathology, supported by a targeted immunohistochemical panel (showing calretinin, WT1, D2-40, and CK7 positivity and loss of BAP1), established the diagnosis of LEPM. Despite an apparently localized presentation and complete resection, early peritoneal recurrence developed on follow-up imaging, prompting adjuvant systemic therapy and cytoreductive surgery (CRS). This report underscores that LEPM should be considered in the differential diagnosis of a solitary pelvic mass, highlights the importance of cross-sectional imaging combined with a specific immunohistochemical panel for distinguishing it from gynecological tumors and gastrointestinal stromal tumor (GIST), and emphasizes the need for close follow-up even when the disease appears localized.

Copyright © 2026, Carvalho et al.

In plain English

This is a case report of one patient with localized epithelioid peritoneal mesothelioma, a rare form of mesothelioma of the abdominal lining that appears as a single, well-defined mass. A 76-year-old woman had a pelvic mass found on a routine transvaginal ultrasound in February 2026. The article states she had no known history of asbestos exposure. Her CA 125 blood marker was mildly raised (36.2 U/mL), and gynecological cancer was first suspected. MRI showed a 5 cm mass clearly separated from the uterus and left ovary. Surgeons removed a 5 cm tumor arising from the small bowel, and omental biopsies were negative. Tissue staining (calretinin, WT1, D2-40 and CK7 positive, BAP1 lost) confirmed epithelioid mesothelioma. A CT scan about three months after surgery showed two new peritoneal implants, the larger 2 cm, and the care team decided to proceed with systemic therapy and cytoreductive surgery. The authors concluded that this tumor should be considered when a single pelvic mass is found. They also concluded that early recurrence can occur even after complete removal, making close imaging follow-up essential.

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 (one patient)
• Who was studied: One 76-year-old woman with no symptoms, referred to the authors' institution in Portugal in February 2026 after a pelvic mass was found incidentally
• Exposure: No known history of asbestos exposure
• Main results:
  • The patient's CA 125 was mildly elevated at 36.2 U/mL.
  • MRI showed clear cleavage planes between the 5 cm mass and both the uterus and the left ovary, arguing against a gynecological origin.
  • At surgery, a 5 cm tumor arising from the antimesenteric border of the small bowel was found and completely removed. Omental biopsies were negative for tumor.
  • Immunohistochemistry showed calretinin, WT1, D2-40 and CK7 expression with loss of BAP1, confirming epithelioid mesothelioma. SOX17, CD117 and DOG1 were negative.
  • A CT scan about three months after surgery (June 2026) showed two new peritoneal implants, the larger measuring 2 cm, consistent with early peritoneal recurrence.
  • After the recurrence, a multidisciplinary decision was made to proceed with adjuvant systemic therapy and cytoreductive surgery.
• The authors' conclusion: The authors concluded that localized epithelioid peritoneal mesothelioma should be included in the differential diagnosis of a solitary pelvic mass, and that early peritoneal recurrence can occur even when disease appears localized and is completely removed. They concluded that close imaging surveillance is therefore essential.

Topics

Medical terms in this study, explained in our Lexicon: Epithelioid, Peritoneal Mesothelioma, Ascites, Ultrasound, Histopathology, Calretinin, Podoplanin (D2-40), BAP1.

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