FDG and FAPI PET-based response evaluation to reduced-dose nivolumab in pleural mesothelioma: A case report

Our plain-English summary of FDG and FAPI PET-based response evaluation to reduced-dose nivolumab in pleural mesothelioma: A case report, by M. Bentestuen, A.H. Thostrup, W.M. Szejniuk, et al (Clinical Physiology and Functional Imaging, 2026).

The study

• Authors: M. Bentestuen, A.H. Thostrup, W.M. Szejniuk, Z. Takacs-Szabo, T.L. Rasmussen, H.D. Zacho
• Journal: Clinical Physiology and Functional Imaging
• Published: 2026;46(2):e70053
• Type of article: Case report
• Read it: PubMed · Publisher · Free full text

Abstract

Reliable tools for objective response assessment are essential in pleural mesothelioma treated with immunotherapy. We report on a 75-year-old man with sarcomatoid pleural mesothelioma who received a reduced nivolumab dose after developing a hypersensitivity reaction during the first infusion. CT, [18F]FDG PET/CT and [68Ga]Ga-Fibroblast activation protein inhibitor-46 (FAPI) PET/CT were performed before and after treatment. Despite the reduced dose, the patient experienced clear clinical benefit, and follow-up imaging demonstrated substantial morphological and metabolic improvement across all imaging modalities. This case offers an unique opportunity to directly compare response assessment across three complimentary imaging modalities.

© 2026 The Author(s). Clinical Physiology and Functional Imaging published by John Wiley & Sons Ltd on behalf of Scandinavian Society of Clinical Physiology and Nuclear Medicine.

In plain English

This case report described one 75-year-old man with sarcomatoid pleural mesothelioma. He had 10 years of occupational asbestos exposure as a bricklayer. Both attempts to give him nivolumab were stopped because of hypersensitivity reactions. He was estimated to have received 50% of the planned nivolumab dose and none of the planned ipilimumab. He had CT and two kinds of PET/CT scan (FDG and the newer tracer FAPI) before and after treatment. Follow-up CT showed partial response, with a mean 36% reduction in diameter across eight target lesions. In one pleural lesion, peak uptake fell 62% on FDG and 72% on FAPI. In another, FDG uptake fell 22% while FAPI uptake rose 14%. Measured tumour volume fell 97% on FDG PET and 94% on FAPI PET. About three months after diagnosis he was in good general health and had gained 4 to 5 kg. The authors concluded that even a low dose of nivolumab can show high efficacy in a patient with sarcomatoid pleural mesothelioma. They noted there was no confirmatory reference standard for response and no standardized FAPI response criteria.

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 75-year-old man with sarcomatoid pleural mesothelioma, who took part in the FAPI-PM clinical trial
• Exposure: 10 years of occupational asbestos exposure as a bricklayer (fiber type not stated). The treatment studied was a reduced dose of nivolumab: about 50% of the planned dose, and none of the planned ipilimumab.
• Main results:
  • Both treatment attempts were stopped because of hypersensitivity reactions. The patient was estimated to have received 50% of the planned nivolumab dose and none of the ipilimumab.
  • At baseline, FDG PET/CT showed moderate uptake in several thoracic lymph nodes (clinical stage T3 N2 M0). FAPI PET/CT showed no lymph node involvement (T3 N0 M0). The lymph nodes were not evaluated further.
  • On follow-up CT, the overall response was partial response by mRECIST v1.1. The mean reduction in diameter across eight target lesions was 36%.
  • Lesion A (upper medial pleura): near complete response on FDG PET, with a 62% reduction in FDG SULpeak (4.17 to 1.60). FAPI SULpeak fell 72% (8.40 to 2.37).
  • Lesion B (dorsomedial pleura): stable disease. FDG SULpeak fell 22% (5.56 to 4.35), while FAPI SULpeak rose 14% (7.45 to 8.49).
  • Volumetric analysis showed reductions in molecular imaging tumour volume of 97% on FDG PET and 94% on FAPI PET. Volume intensity product fell 97% on FDG PET and 95% on FAPI PET.
  • At clinical follow-up about 3 months after diagnosis, the patient was in general good health (performance status 1) and had gained 4 to 5 kg.
• The authors' conclusion: The authors concluded that this case illustrates that even a low dose of nivolumab can show high efficacy in a patient with sarcomatoid pleural mesothelioma. They also said it gives insight into similarities and differences between the FDG and FAPI PET tracers.
• Limitations the authors state:
  • There was no confirmatory reference standard for treatment response. The overall 'partial response' assessment relied on agreement between mRECIST CT, FDG PET and clinical follow-up.
  • No standardized criteria exist for FAPI PET response assessment, and the observed FAPI changes are of unknown clinical value.

Topics

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

Medical terms in this study, explained in our Lexicon: Nivolumab (Opdivo), Pleural Mesothelioma, Immunotherapy, Sarcomatoid, Fibroblast.

Related studies

• Comparison of FDG-PET/CT and CT for evaluation of tumor response to nivolumab plus ipilimumab combination therapy and prognosis prediction in patients with unresectable malignant pleural mesothelioma — K. Kitajima, K. Kuribayashi, et al. (2024)
• Outcome prediction based on [18F]FDG PET/CT in patients with pleural mesothelioma treated with ipilimumab and nivolumab +/- UV1 telomerase vaccine — S. Thunold, E. Hernes, et al. (2025)
• CONFIRM: a double-blind, placebo-controlled phase III clinical trial investigating the effect of nivolumab in patients with relapsed mesothelioma: study protocol for a randomised controlled trial — D.A. Fennell, E. Kirkpatrick, et al. (2018)
• Correlation between immune-related adverse events and therapeutic effects of nivolumab in patients with malignant pleural mesothelioma — H. Yoneda, H. Nokihara, et al. (2021)
• Efficacy of Nivolumab in Chemotherapy-Resistant Mesothelioma of the Tunica Vaginalis Testis: A Case Report — H. Koyanagi, T. Kawahara, et al. (2026)
• Whole-Body MRI: Comparison of Its Capability for TNM Staging of Malignant Pleural Mesothelioma With That of Coregistered PET/MRI, Integrated FDG PET/CT, and Conventional Imaging — Y. Ohno, M. Yui, et al. (2019)

Browse return to medical research.