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Peer-reviewedCC BY 4.0Frontiers in Oncology

Multifocal FDG-avid pancreatic pseudomasses mimicking metastases during pembrolizumab for axillary recurrence of triple-negative breast cancer: a case report of immune-related pancreatitis

  • Paul Matte1
  • Claire Charpignon2
  • Vincent Servois3
  • Virginie Huchet4
  • Bruno Buecher5
  • Caroline Malhaire6
  • Jean-Yves Pierga1
  • Luc Cabel1
  • Delphine Loirat1
6 affiliations
  1. 1Department of Medical Oncology, Institute of Women's Cancers, Institut Curie
  2. 2Department of Gastroenterology, Institut Mutualiste Montsouris
  3. 3Department of Radiology, Institut Curie, Paris Sciences et Lettres (PSL) Research University
  4. 4Department of Nuclear Medicine, Institut Curie
  5. 5Departments of Genetics and of Surgical Oncology, Institut Curie, Paris Sciences et Lettres (PSL) Research University
  6. 6Department of Radiology, Laboratoire d'Imagerie Translationnelle en Oncologie (LITO), Inserm U1288, Institut Curie
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Abstract

Background: Immune checkpoint inhibitors (ICIs) are associated with a wide spectrum of immune-related adverse events (irAEs), reflecting enhanced immune activation. Pancreatic involvement is rare and typically presents as asymptomatic hyperlipasemia or diffuse inflammatory changes. Focal or multifocal mass-like presentations are uncommon and may mimic pancreatic malignancy, posing a significant diagnostic challenge.

Case presentation: We report the case of a 48-year-old woman treated with Pembrolizumab and Paclitaxel for axillary recurrence of triple-negative breast cancer. After four cycles, FDG PET/CT demonstrated a complete metabolic response at the initial tumor site but revealed new multifocal hypermetabolic pancreatic lesions. Magnetic resonance imaging confirmed multiple pancreatic masses, raising suspicion of metastatic disease or dissociated response. Endoscopic ultrasound-guided fine-needle aspiration at two concordant pancreatic sites showed neutrophil-predominant inflammatory infiltration without malignant cells, consistent with immune-related pancreatic injury. The patient subsequently developed symptoms of exocrine pancreatic insufficiency, which improved after concomitant initiation of pancreatic enzyme replacement therapy and corticosteroid tapering, with the relative contribution of each not clearly distinguishable. Follow-up imaging demonstrated complete resolution of pancreatic lesions.

Discussion: This case highlights a rare mass-forming (pseudotumoral) phenotype of ICI-related pancreatic injury (ICI-PI), presenting as multifocal FDG-avid pancreatic pseudomasses. Such findings may represent a major pitfall in PET/CT interpretation under immunotherapy, particularly in the context of otherwise favorable oncologic response. Histopathological confirmation is critical to distinguish immune-mediated inflammation from metastatic disease. This observation supports the concept of organ-specific immune dysregulation driven by ICIs and expands the radiological spectrum of pancreatic irAEs.

Conclusion: Multifocal FDG-avid pancreatic lesions occurring during immunotherapy should raise suspicion for immune-related pancreatic injury (ICI-PI), especially in the absence of systemic progression. Early recognition is essential to avoid misdiagnosis and inappropriate treatment decisions.

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Cite

BibTeXRIS
BibTeX
@article{matte2026multifocal,
  title = {{Multifocal FDG-avid pancreatic pseudomasses mimicking metastases during pembrolizumab for axillary recurrence of triple-negative breast cancer: a case report of immune-related pancreatitis}},
  author = {Paul Matte and Claire Charpignon and Vincent Servois and Virginie Huchet and Bruno Buecher and Caroline Malhaire and Jean-Yves Pierga and Luc Cabel and Delphine Loirat},
  journal = {Frontiers in Oncology},
  year = {2026},
  month = oct,
  doi = {10.3389/fonc.2026.1940160},
  url = {https://www.frontiersin.org/articles/10.3389/fonc.2026.1940160/full},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Multifocal FDG-avid pancreatic pseudomasses mimicking metastases during pembrolizumab for axillary recurrence of triple-negative breast cancer: a case report of immune-related pancreatitis
AU  - Paul Matte
AU  - Claire Charpignon
AU  - Vincent Servois
AU  - Virginie Huchet
AU  - Bruno Buecher
AU  - Caroline Malhaire
AU  - Jean-Yves Pierga
AU  - Luc Cabel
AU  - Delphine Loirat
PY  - 2026
DA  - 2026/10/15
JO  - Frontiers in Oncology
DO  - 10.3389/fonc.2026.1940160
UR  - https://www.frontiersin.org/articles/10.3389/fonc.2026.1940160/full
AB  - Background: Immune checkpoint inhibitors (ICIs) are associated with a wide spectrum of immune-related adverse events (irAEs), reflecting enhanced immune activation. Pancreatic involvement is rare and typically presents as asymptomatic hyperlipasemia or diffuse inflammatory changes. Focal or multifocal mass-like presentations are uncommon and may mimic pancreatic malignancy, posing a significant diagnostic challenge.  Case presentation: We report the case of a 48-year-old woman treated with Pembrolizumab and Paclitaxel for axillary recurrence of triple-negative breast cancer. After four cycles, FDG PET/CT demonstrated a complete metabolic response at the initial tumor site but revealed new multifocal hypermetabolic pancreatic lesions. Magnetic resonance imaging confirmed multiple pancreatic masses, raising suspicion of metastatic disease or dissociated response. Endoscopic ultrasound-guided fine-needle aspiration at two concordant pancreatic sites showed neutrophil-predominant inflammatory infiltration without malignant cells, consistent with immune-related pancreatic injury. The patient subsequently developed symptoms of exocrine pancreatic insufficiency, which improved after concomitant initiation of pancreatic enzyme replacement therapy and corticosteroid tapering, with the relative contribution of each not clearly distinguishable. Follow-up imaging demonstrated complete resolution of pancreatic lesions.  Discussion: This case highlights a rare mass-forming (pseudotumoral) phenotype of ICI-related pancreatic injury (ICI-PI), presenting as multifocal FDG-avid pancreatic pseudomasses. Such findings may represent a major pitfall in PET/CT interpretation under immunotherapy, particularly in the context of otherwise favorable oncologic response. Histopathological confirmation is critical to distinguish immune-mediated inflammation from metastatic disease. This observation supports the concept of organ-specific immune dysregulation driven by ICIs and expands the radiological spectrum of pancreatic irAEs.  Conclusion: Multifocal FDG-avid pancreatic lesions occurring during immunotherapy should raise suspicion for immune-related pancreatic injury (ICI-PI), especially in the absence of systemic progression. Early recognition is essential to avoid misdiagnosis and inappropriate treatment decisions.
SN  - 2234-943X
ER  -