ALK positive malignant peritoneal mesothelioma mimicking inflammatory myofibroblastic tumour: a diagnostic pitfall

Our plain-English summary of ALK positive malignant peritoneal mesothelioma mimicking inflammatory myofibroblastic tumour: a diagnostic pitfall, by A. Louw, C. Wallace, S.M. Chai, et al (Pathology, 2020).

The study

• Authors: A. Louw, C. Wallace, S.M. Chai, B. Amanuel, D.D. Wong
• Journal: Pathology
• Published: 2020;52(6):719-722
• Type of article: Case report, Letter
• Read it: PubMed · Publisher

In plain English

This letter is a case report about one patient. A 41-year-old man had two weeks of right lower abdominal pain and no history of prior asbestos exposure or cancer. A CT scan showed a 43 mm lump, and surgeons removed it from the small bowel mesentery, the tissue that holds the small bowel in place. Under the microscope and on several stains, the tumour looked like inflammatory myofibroblastic tumour (IMT), a different tumour. It overproduced ALK protein, and gene testing found an ALK-FN1 gene fusion. However, the tumour cells also stained diffusely for cytokeratins and for mesothelial markers (calretinin, WT1, D2-40). Further testing showed homozygous loss of the CDKN2A gene and evidence of monosomy 22q. The final diagnosis was malignant peritoneal mesothelioma. He then had four cycles of cisplatin and pemetrexed and was disease-free 5 months after surgery. The authors stated that, to their knowledge, this fusion had not been reported before in peritoneal mesothelioma. They concluded that the overlap with IMT is a diagnostic pitfall, and that ALK fusions point to possible treatment with ALK inhibitors.

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, published as a letter (correspondence)
• Who was studied: One 41-year-old man with a 2-week history of right iliac fossa (right lower abdominal) pain. The authors are from pathology services in Western Australia. Dates are not given.
• Exposure: No asbestos exposure: the patient had no history of prior asbestos exposure. The study concerns the tumour's microscopic, staining and genetic features, not an exposure.
• Main results:
  • A 43 mm lobulated fibrous mass was found in the small bowel mesentery, not attached to the bowel wall.
  • Features resembled inflammatory myofibroblastic tumour. The tumour showed diffuse ALK protein over-expression and an ALK gene re-arrangement on FISH. Next generation sequencing confirmed an ALK-FN1 fusion.
  • Tumour cells stained diffusely for mesothelial markers calretinin, WT1 (nuclear) and D2-40.
  • BAP1 expression was retained in the tumour.
  • FISH testing showed homozygous loss of CDKN2A and evidence of monosomy 22q. On this basis, malignant peritoneal mesothelioma with an ALK-FN1 fusion was diagnosed.
  • After four cycles of adjuvant cisplatin and pemetrexed, the patient remained disease-free 5 months after the operation.
  • The authors stated that, to their knowledge, the ALK-FN1 fusion had not previously been reported in malignant peritoneal mesothelioma.
• The authors' conclusion: The authors concluded that this case's overlap with inflammatory myofibroblastic tumour is a diagnostic pitfall with significant clinical implications, given differences in prognosis and management. They also said that ALK fusions in peritoneal mesothelioma provide a promising treatment avenue using ALK inhibitors.

Topics

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

Medical terms in this study, explained in our Lexicon: Peritoneal Mesothelioma.

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• Identification of ALK Rearrangements in Malignant Peritoneal Mesothelioma — Y.P. Hung, F. Dong, et al. (2018)
• Hibernoma-like Changes and TFE3 Expression in Mesothelioma Mimicking TFE3-Translocation Renal Cell Carcinoma: A Diagnostic Pitfall — D. Hoton, M. Luyckx, et al. (2021)
• Malignant peritoneal mesothelioma mimicking mesenteric inflammatory disease — A. Andrion, E. Feyles, et al. (1994)
• Immunoreactivity for calretinin and keratins in desmoid fibromatosis and other myofibroblastic tumors: a diagnostic pitfall — S. Barak, Z. Wang, et al. (2012)
• Anaplastic lymphoma kinase (ALK) translocation in paediatric malignant peritoneal mesothelioma: a case report of novel ALK-related tumour spectrum — K. Loharamtaweethong, N. Puripat, et al. (2016)

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