Loco-regional staging of malignant pleural mesothelioma by integrated 18F-FDG PET/MRI

Our plain-English summary of Loco-regional staging of malignant pleural mesothelioma by integrated 18F-FDG PET/MRI, by D.J. Murphy, S.M. Mak, A. Mallia, et al (European Journal of Radiology, 2019).

The study

• Authors: D.J. Murphy, S.M. Mak, A. Mallia, S. Jeljeli, J.J. Stirling, V. Goh, A. Bille, G.J.R. Cook
• Journal: European Journal of Radiology
• Published: 2019;115:46-52
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Aim: To examine the performance of 18F-FDG PET/MRI in the loco-regional staging of malignant pleural mesothelioma (MPM).

Methods: Consecutive subjects with MPM undergoing pre-operative staging with 18F-FDG PET/CT who underwent a same day integrated 18F-FDG PET/MRI were prospectively studied. Clinical TNM staging (AJCC 7th edition) was performed separately and in consensus by two readers on the 18F-FDG PET/MRI studies, and compared with staging by 18F-FDG PET/CT, and with final pathological stage, determined by a combination of intra-operative and histological findings.

Results: 10 subjects (9 male, mean age 68 years) with biopsy-proven MPM (9 epithelioid tumours, 1 biphasic) were included. One subject underwent neo-adjuvant chemotherapy between imaging and surgery and was excluded from the clinical versus pathological stage analysis. Pathological staging was concordant with staging by 18F-FDG PET/MRI in 67% (n = 6) of subjects, and with 18F-FDG PET/CT staging in 33% (n = 3). Pathological T stage was concordant with 18F-FDG PET/MRI in 78% (n = 7), and with 18F-FDG PET/CT in 33% (n = 3) of subjects. Pathological N stage was concordant with both 18F-FDG PET/MRI and 18F-FDG PET/CT in 78% (n = 7) of cases. No subject had metastatic disease. There was good inter-observer agreement for overall PET/MRI staging (weighted kappa 0.63) with moderate inter-reader agreement for T staging (weighted kappa 0.59). All 6 subjects with prior talc pleurodesis demonstrated mismatch between elevated FDG uptake and restricted diffusion in areas of visible talc deposition.

Conclusion: Clinical MPM staging by 18F-FDG PET/MRI is feasible, and potentially provides more accurate loco-regional staging than PET/CT, particularly in T staging.

Copyright © 2019 Elsevier B.V. All rights reserved.

In plain English

This prospective single-centre study in London tested whether a scanner that takes PET and MRI images together (FDG PET/MRI) can stage malignant pleural mesothelioma before surgery. Ten patients (9 men, 1 woman, mean age 68) with biopsy-proven disease had a standard FDG PET/CT scan and, the same day, a PET/MRI scan. Two radiologists staged the tumours on PET/MRI. The results were compared with PET/CT and with the final stage found at surgery and on tissue examination. Asbestos exposure was not studied. One patient had chemotherapy before surgery and was left out of that comparison. Among the other 9, PET/MRI matched the surgical stage in 6 (67%) and PET/CT in 3 (33%). For local tumour spread (T stage), PET/MRI matched in 7 (78%) versus 3 (33%) for PET/CT. Both matched lymph node stage in 7 (78%). In all 6 patients with earlier talc pleurodesis, talc areas showed high FDG uptake but no restricted diffusion on MRI. The authors concluded PET/MRI appears feasible and may be superior to PET/CT, particularly for T stage. They noted the small, single-site sample.

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: Prospective single-centre imaging study comparing integrated FDG PET/MRI with FDG PET/CT, using final pathological stage as the reference standard
• Who was studied: 10 patients (9 men, 1 woman, mean age 68, range 51 to 73) with biopsy-proven malignant pleural mesothelioma (9 epithelioid, 1 biphasic) who were potential surgical candidates, referred to the King's College London & Guy's and St Thomas' PET Centre, London; the study began in 2015
• Exposure: No asbestos exposure was studied. What was studied was imaging: a same-day integrated FDG PET/MRI scan done right after the clinical FDG PET/CT scan, both staged by the AJCC 7th edition TNM system
• Main results:
  • In the 9 patients who went straight to surgery, overall stage on PET/MRI matched pathological stage in 6 (67%).
  • In the same 9 patients, overall stage on PET/CT matched pathological stage in 3 (33%) and did not match in 6 (67%).
  • T stage matched pathology in 7 of 9 (78%) on PET/MRI versus 3 (33%) on PET/CT
  • N stage matched pathology in 7 of 9 (78%) for both PET/MRI and PET/CT
  • Agreement between the two PET/MRI readers was good for overall stage (weighted kappa 0.63). It was moderate for T stage (weighted kappa 0.59) and N stage (weighted kappa 0.52).
  • No patient had metastatic disease on imaging or pathology
  • No significant correlation was found between tumour SUVmax and ADCmean (r = 0.15, p = 0.7)
  • Six patients (60%) had prior talc pleurodesis. In these 6, talc areas had higher FDG uptake than tumour areas without visible talc (mean SUVmax 7.4 versus 4.9), but the difference was not statistically significant (p = 0.06).
  • In every patient with prior talc pleurodesis, talc areas showed a mismatch between FDG uptake on PET and diffusion restriction on MRI
• The authors' conclusion: The authors concluded that integrated FDG PET/MRI appears feasible for loco-regional staging of malignant pleural mesothelioma and may be superior to FDG PET/CT, particularly for T stage. They also said that DWI-FDG mismatch may help tell talc-related uptake from tumour after talc pleurodesis, but this needs further study in a larger cohort.
• Limitations the authors state:
  • Single-site study with a small sample size
  • The CT part of the PET/CT was done without intravenous contrast, a potential source of bias in comparing the two methods
  • Inter-observer agreement for PET/CT staging was not examined
  • Staging used the 7th edition of the AJCC TNM system although the 8th edition is now in use; the authors considered this unlikely to change results significantly
  • Only axial MRI images were acquired; readers felt coronal and sagittal images would have helped staging
  • The talc mismatch finding is only an observation needing investigation in a larger cohort

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: Staging, Pleural Mesothelioma, TNM Staging, AJCC, Biopsy, Epithelioid, Biphasic Mesothelioma, Chemotherapy.

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