Zirconium-89 Girentuximab PET-CT Images Rare Peritoneal Mesothelioma in First Report

A case report published in EJNMMI Research describes the first known use of CAIX-targeted PET-CT imaging in malignant epithelioid peritoneal mesothelioma, a rare cancer arising from the mesothelial lining of the peritoneal cavity. The imaging used [89Zr]Zr-girentuximab, a radiolabelled antibody that binds carbonic anhydrase IX, a hypoxia-associated transmembrane enzyme commonly expressed in this tumour type.

The patient, a woman who had initially been misdiagnosed with hepatocellular carcinoma, underwent an imaging work-up as part of the ELEGANCE clinical trial (NCT06735560). Conventional FDG PET-CT revealed intense hypermetabolism of multilobar lesions in hepatic segment VIII, together with diffuse anterior parietal peritoneal extension.

The CAIX-targeted tracer then showed intense uptake of the hepatic lesion in segment VIII, demonstrating that the antibody accumulated in the tumour tissue in vivo. This molecular imaging signal complemented the metabolic information from FDG PET-CT by reporting on a specific tumour-associated antigen rather than glucose metabolism alone.

A subsequent laparoscopy revealed adhesions in the right hypochondrium, extending throughout the subumbilical region, and diffuse unresectable peritoneal carcinomatosis. These operative findings established the extent of disease and its inoperability at that stage.

The definitive diagnosis came from histopathology. After review of the initial biopsy specimens, the final diagnosis was revised to malignant epithelioid peritoneal mesothelioma. Immunohistochemical analysis of the tumour showed moderate to strong CAIX staining of the tumour cells, confirming that the molecular target detected by the PET tracer was indeed present in the tissue.

The correspondence between the tracer uptake seen on [89Zr]Zr-girentuximab PET and the CAIX expression demonstrated by immunohistochemistry is the central technical observation of the report. It suggests that girentuximab-based imaging can visualise CAIX-expressing peritoneal mesothelioma lesions, although this conclusion rests on a single patient.

The authors state that, to their knowledge, this is the first report of CAIX-targeted PET/CT in malignant peritoneal mesothelioma. They argue that the finding supports the potential role of this imaging approach in innovative theranostic strategies, in which the same target could be used for both diagnosis and targeted therapy.

As a case report of one patient, the study does not establish diagnostic accuracy, sensitivity or clinical benefit for CAIX-targeted imaging in this disease. The imaging was performed within a clinical trial framework, and broader evidence from larger cohorts would be needed to determine whether [89Zr]Zr-girentuximab PET-CT becomes a useful tool in the work-up of malignant peritoneal mesothelioma or in selecting patients for CAIX-directed theranostics.

Subject of Research: First reported CAIX-targeted zirconium-89 girentuximab PET-CT imaging of malignant epithelioid peritoneal mesothelioma

Article Title: [89Zr]Zr-girentuximab PET-CT imaging of a malignant epithelioid peritoneal mesothelioma

Article References: Touchefeu, Y., Loussouarn, D., François, C., Bardy, R., David, A., Sagan, C., Vilgrain, V., Kraeber-Bodéré, F., & Bailly, C. (2026). [89Zr]Zr-girentuximab PET-CT imaging of a malignant epithelioid peritoneal mesothelioma. EJNMMI Research. https://doi.org/10.1186/s13550-026-01526-5

Image Credits: AI Generated

DOI: 10.1186/s13550-026-01526-5

Keywords: PET-CT, girentuximab, carbonic anhydrase IX, peritoneal mesothelioma, case report, molecular imaging, theranostics, zirconium-89, EJNMMI Research, CAIX, Zr-girentuximab, imaging