In-vivo imaging of methionine metabolism in patients with suspected malignant pleural mesothelioma

Our plain-English summary of In-vivo imaging of methionine metabolism in patients with suspected malignant pleural mesothelioma, by E. Lopci, P. Novellis, A. Testori, et al (Nuclear Medicine Communications, 2019).

The study

• Authors: E. Lopci, P. Novellis, A. Testori, D. Rahal, E. Voulaz, E. Bottoni, G.M. Ferraroli, A. Crepaldi, G.L. Ceresoli, M. Perrino, A. Castello, M. Alloisio, G. Veronesi, P.A. Zucali
• Journal: Nuclear Medicine Communications
• Published: 2019;40(11):1179-1186
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: In-vivo characterization of malignant pleural mesothelioma (MPM) with C-methionine PET/computed tomography (MET PET).

Methods: Between September 2014 and February 2016, 30 consecutive patients with clinical suspicion of MPM were prospectively recruited. The study was approved and registered at www.clinicaltrials.gov (NCT02519049). Patients were evaluated at baseline with MET PET (experimental) and fluorine-18 fluorodeoxyglucose PET/computed tomography (FDG PET) (standard). Principal parameters analyzed were SUVmax, SUVmean, metabolic tumor volume (MTV), and metabolic tumor burden (MTB = MTV ×SUVmean). The reference standard for diagnostic performance was based on histology.

Results: The presence of malignancy was confirmed in 29/30 patients: 23 (76.6%) with MPM (20 epithelioid, two biphasic, and one sarcomatoid), five (16.6%) with adenocarcinoma of the lung, and one (3.3%) with an undifferentiated carcinoma. In one case, diagnosis was benign pleural inflammation. All tumors showed increased uptake of C-methionine: median SUVmax, SUVmean, MTV, and MTB were, respectively, 5.70 [95% confidence interval (CI): 4.51-6.79], 3.15 (95% CI: 2.71-3.40), 33.85 (95% CI: 14.08-66.64), and 105.25 (95% CI: 41.77-215.25). Pathology data revealed MTV and MTB to be significantly higher in nonepithelioid histology (P < 0.05). The other parameters showed a homogeneous distribution across the tumor types. Overall, MET PET identified 49 lymph nodes, compared with 34 nodes on FDG PET, demonstrating a sensitivity of 91% (95% CI: 80-96%), a positive predictive value of 92% (95% CI: 82- 97%), and an accuracy of 85% (P = 0.0042).

Conclusions: MET PET is able to characterize MPM lesions regardless of histology. This technique shows higher sensitivity than FDG PET for the identification of secondary lymph nodes.

In plain English

This prospective study in Rozzano, Milan, Italy, scanned 30 consecutive patients suspected of malignant pleural mesothelioma between September 2014 and February 2016. Each had a standard FDG PET/CT scan and an experimental carbon-11 methionine (MET) scan, then a biopsy. Asbestos exposure was not examined. Biopsies found cancer in 29 of 30 patients: 23 mesotheliomas (20 epithelioid, two biphasic, one sarcomatoid), five lung adenocarcinomas and one undifferentiated lung carcinoma. All tumors took up methionine. Uptake values did not differ significantly by tumor type. Tumor-volume measures were significantly higher for non-epithelioid tumors in some comparisons. The authors counted 54 involved lymph node sites, judged by CT and follow-up scans rather than biopsy. MET PET detected 49 and FDG PET 34. For lymph nodes, sensitivity was 91% (95% confidence interval 80% to 96%) for MET PET versus 59% (45% to 71%) for FDG PET, and specificity 20% (11% to 33%) versus 75% (62% to 85%), and accuracy 85% versus 60%. The accuracy difference was statistically significant. The authors concluded that MET PET was more sensitive for lymph nodes and called the trial preliminary.

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 diagnostic imaging study comparing an experimental PET tracer (11C-methionine) with the standard tracer (18F-FDG), with biopsy as the reference for the pleura
• Who was studied: 30 consecutive patients with pleural effusion suspected to be malignant pleural mesothelioma, recruited September 2014 to February 2016 at Humanitas Clinical and Research Center, Rozzano, Milan, Italy. 25 were men and 5 women; median age was 72 (range 36 to 86).
• Exposure: Asbestos exposure was not studied. The study examined two imaging tests: a baseline 18F-FDG PET/CT and a baseline 11C-methionine PET/CT, done about 24 to 48 hours apart, followed by video-assisted thoracoscopy for biopsy.
• Main results:
  • Biopsy confirmed cancer in 29 of 30 patients: 23 (76.6%) had mesothelioma (20 epithelioid, 2 biphasic, 1 sarcomatoid), 5 (16.6%) had lung adenocarcinoma and 1 (3.3%) had an undifferentiated lung carcinoma. One patient had benign pleural inflammation.
  • All tumors showed increased uptake of 11C-methionine.
  • On MET PET, the uptake values (SUVmax and SUVmean) did not differ significantly by tumor histology.
  • On MET PET, metabolic tumor volume (MTV) did not differ significantly in the analysis of all 29 cancer patients (P = 0.199). Among the 23 mesothelioma patients, MTV was significantly higher in non-epithelioid tumors (P = 0.045).
  • On MET PET, metabolic tumor burden (MTB) differed significantly by histology both among all 29 cancer patients (P = 0.008) and among the 23 mesothelioma patients (P = 0.035).
  • 54 lymph node stations in 28 patients were counted as involved. MET PET showed activity in 49 (90.7%) and FDG PET in 34 (63%).
  • For lymph nodes, MET PET had specificity 20% (95% CI 11% to 33%), PPV 92% (95% CI 82% to 97%), negative predictive value 17% (95% CI 9% to 29%) and accuracy 85%.
  • For lymph nodes, FDG PET had sensitivity 59% (95% CI 45% to 71%), specificity 75% (95% CI 62% to 85%), PPV 97% (95% CI 88% to 100%), negative predictive value 11% (95% CI 5% to 22%) and accuracy 60%.
  • MET PET had a lymph node sensitivity of 91% (95% CI 80 to 96%) and a lymph node accuracy of 85%. The authors report that this accuracy was significantly higher than FDG PET's (P = 0.0042).
  • FDG showed higher uptake values than methionine.
• The authors' conclusion: The authors concluded that MET PET performed comparably to FDG PET for pleural lesions and showed greater sensitivity for identifying secondary lymph nodes, suggesting a potential advantage especially in nodal staging. They described the trial as preliminary.
• Limitations the authors state:
  • Lymph nodes were not examined by pathology. Nodal involvement was judged from contrast-enhanced CT and serial imaging.
  • The small number of cases in each group may explain why no uptake differences were seen between tumor types.
  • Only one case of benign pleural inflammation was included, so no conclusions could be drawn about inflammation and methionine uptake. That case was falsely positive on all imaging.
  • High methionine uptake in the liver made MET PET suboptimal for pleural lesions in the lower right chest.
  • The authors called the trial preliminary.

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: Pleural Mesothelioma, Tumor Burden, Histology, Epithelioid, Biphasic Mesothelioma, Sarcomatoid, Adenocarcinoma, Carcinoma.

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