Imaging in pleural mesothelioma: A review of Imaging Research Presented at the 9th International Meeting of the International Mesothelioma Interest Group

Fibroblast Activation Protein-Directed Imaging Outperforms 18F-FDG PET/CT in Malignant Mesothelioma: A Prospective, Single-Center, Observational Trial

The fibroblast activation protein (FAP) is highly expressed in tumor and stromal cells of mesothelioma and thus is an interesting imaging and therapeutic target. Previous data on PET imaging with radiolabeled FAP inhibitors (FAPIs) suggest high potential for superior tumor detection. Here, we report the data of a large malignant pleural mesothelioma cohort within a 68Ga-FAPI46 PET observational trial (NCT04571086). Methods: Of 43 eligible patients with suspected or proven malignant mesothelioma, 41 could be included in the data analysis of the 68Ga-FAPI46 PET observational trial. All patients underwent 68Ga-FAPI46 PET/CT, contrast-enhanced CT, and 18F-FDG PET/CT. The primary study endpoint was the association of 68Ga-FAPI46 PET uptake intensity and histopathologic FAP expression. Furthermore, secondary endpoints were detection rate and sensitivity, specificity, and positive and negative predictive values as compared with 18F-FDG PET/CT. Datasets were interpreted by 2 masked readers. Results: The primary endpoint was met, and the association between 68Ga-FAPI46 SUVmax or SUVpeak and histopathologic FAP expression was significant (SUVmax: r = 0.49, P = 0.037; SUVpeak: r = 0.51, P = 0.030).68Ga-FAPI46 and 18F-FDG showed similar sensitivity by histopathologic validation on a per-patient (100.0% vs. 97.3%) and per region (98.0% vs. 95.9%) basis. Per-region analysis revealed higher 68Ga-FAPI46 than 18F-FDG specificity (81.1% vs. 36.8%) and positive predictive value (87.5% vs. 66.2%). Conclusion: We confirm an association of 68Ga-FAPI46 uptake and histopathologic FAP expression in mesothelioma patients. Additionally, we report high sensitivity and superior specificity and positive predictive value for 68Ga-FAPI46 versus 18F-FDG.

Metabolic rewiring and redox alterations in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a rare malignancy of mesothelial cells with increasing incidence, and in many cases, dismal prognosis due to its aggressiveness and lack of effective therapies. Environmental and occupational exposure to asbestos is considered the main aetiological factor for MPM. Inhaled asbestos fibres accumulate in the lungs and induce the generation of reactive oxygen species (ROS) due to the presence of iron associated with the fibrous silicates and to the activation of macrophages and inflammation. Chronic inflammation and a ROS-enriched microenvironment can foster the malignant transformation of mesothelial cells. In addition, MPM cells have a highly glycolytic metabolic profile and are positive in 18F-FDG PET analysis. Loss-of-function mutations of BRCA-associated protein 1 (BAP1) are a major contributor to the metabolic rewiring of MPM cells. A subset of MPM tumours show loss of the methyladenosine phosphorylase (MTAP) locus, resulting in profound alterations in polyamine metabolism, ATP and methionine salvage pathways, as well as changes in epigenetic control of gene expression. This review provides an overview of the perturbations in metabolism and ROS homoeostasis of MPM cells and the role of these alterations in malignant transformation and tumour progression.

Imaging in pleural mesothelioma: A review of the 14th International Conference of the International Mesothelioma Interest Group

Mesothelioma patients rely on the information their clinical team obtains from medical imaging. Whether x-ray-based computed tomography (CT) or magnetic resonance imaging (MRI) based on local magnetic fields within a patient's tissues, different modalities generate images with uniquely different appearances and information content due to the physical differences of the image-acquisition process. Researchers are developing sophisticated ways to extract a greater amount of the information contained within these images. This paper summarizes the imaging-based research presented orally at the 2018 International Conference of the International Mesothelioma Interest Group (iMig) in Ottawa, Ontario, Canada, held May 2-5, 2018. Presented topics included advances in the imaging of preclinical mesothelioma models to inform clinical therapeutic strategies, optimization of the time delay between contrast administration and image acquisition for maximized enhancement of mesothelioma tumor on CT, an investigation of image-based criteria for clinical tumor and nodal staging of mesothelioma by contrast-enhanced CT, an investigation of methods for the extraction of mesothelioma tumor volume from MRI and the association of volume with patient survival, the use of deep learning for mesothelioma tumor segmentation in CT, and an evaluation of CT-based radiomics for the prognosis of mesothelioma patient survival.

Imaging in pleural mesothelioma: A review of the 13th International Conference of the International Mesothelioma Interest Group

Imaging plays an important role in the detection, diagnosis, staging, response assessment, and surveillance of malignant pleural mesothelioma. The etiology, biology, and growth pattern of mesothelioma present unique challenges for each modality used to capture various aspects of this disease. Clinical implementation of imaging techniques and information derived from images continue to evolve based on active research in this field worldwide. This paper summarizes the imaging-based research presented orally at the 2016 International Conference of the International Mesothelioma Interest Group (iMig) in Birmingham, United Kingdom, held May 1-4, 2016. Presented topics included intraoperative near-infrared imaging of mesothelioma to aid the assessment of resection completeness, an evaluation of tumor enhancement improvement with increased time delay between contrast injection and image acquisition in standard clinical magnetic resonance imaging (MRI) scans, the potential of early contrast enhancement analysis to provide MRI with a role in mesothelioma detection, the differentiation of short- and long-term survivors based on MRI tumor volume and histogram analysis, the response-assessment potential of hemodynamic parameters derived from dynamic contrast-enhanced computed tomography (DCE-CT) scans, the correlation of CT-based tumor volume with post-surgical tumor specimen weight, and consideration of the need to update the mesothelioma tumor response assessment paradigm.

Contemporary Analysis of Prognostic Factors in Patients with Unresectable Malignant Pleural Mesothelioma

INTRODUCTION

Previous prognostic scoring systems for malignant pleural mesothelioma (MPM) included patients managed surgically and predated the use of pemetrexed. We analyzed prognostic factors in a contemporary cohort of patients with unresectable MPM who received pemetrexed-based chemotherapy.

METHODS

This single-institution analysis included patients with MPM who were managed nonsurgically from 2000 to 2013. Variables correlated with overall survival (OS) included sex, performance status (PS), asbestos exposure, tumor laterality, histology, clinical stage, initial positron emission tomography maximum standardized uptake value, hemoglobin level, platelet count, lymphocyte count, white cell and neutrophil counts, treatment type, and clinical benefit from treatment. OS was analyzed by the Kaplan-Meier method, and significance (p < 0.05) of prognostic factors was analyzed by the log-rank test and Cox regression.

RESULTS

A total of 191 patients met the study criteria: median age 71 years (range 46-90), 147 men (77%), 128 epithelioid tumors (67%), and 157 cases of stage III or IV MPM (82%). Median OS for all patients was 13.4 months. According to a univariate analysis, histology (p < 0.001), platelet count (< or = 450,000 versus >450,000, p < 0.001), initial PS (0-1 versus > or = 2), maximum standardized uptake value (< or = 8.1 versus >8.1, p = 0.037), and lymphocyte counts (p = 0.019) were associated with OS. According to a multivariable analysis, only histology, platelet count, and PS were independent prognostic factors. Epithelioid histology, PS, and elevated lymphocyte count at diagnosis were significantly associated with clinical benefit from first-line chemotherapy.

CONCLUSIONS

Our results confirm the significance of elements of the Cancer and Leukemia Group B and European Organisation for Research and Treatment of Cancer prognostic scoring systems, identify factors associated with clinical benefit from chemotherapy, and emphasize the impact of histology and clinical benefit of chemotherapy on outcomes.

Imaging the pleura

Pleural disease is now recognized as an important subspecialty of pulmonary medicine, with increasing provision being made for specialist services and procedures. In response, the field of pleural imaging has advanced in recent years, especially with regard to ultrasound. Salient multimodality imaging techniques are discussed.

Changes in pulmonary function tests predict radiological response to chemotherapy in malignant pleural mesothelioma

OBJECTIVES

Response to chemotherapy in malignant pleural mesothelioma (MPM) is usually evaluated by radiological criteria, but no common agreement exists on their validity, yet. The cytoreductive effect of chemotherapy on pleural thickening may make the lung more expansible, reducing the restrictive ventilatory impairment. The aim of this study was to evaluate the changes in pulmonary function following chemotherapy in patients with MPM and to correlate these findings with radiological changes.

METHODS

Between 2004 and 2011, 62 consecutive patients (74% males, median age 63 years) were prospectively investigated. Modified RECIST criteria were used for radiological evaluation of response to chemotherapy. All patients underwent pulmonary function tests before and after three cycles of platinum-based chemotherapy. Changes between baseline and post-chemotherapy pulmonary function values (Δ) and their differences were assessed by means of Student's paired and unpaired t-test, respectively. Receiver operating characteristic (ROC) curve analysis was performed on spirometric parameters significantly associated with response.

RESULTS

Thirty (48.4%) patients had a radiological stable disease (S), 23 (37.1%) a partial response (R) and 9 (14.5%) a progressive disease (P). ΔFEV1%pred (R: 18.1 ± 18.5%; S: 0.5 ± 9.3%; P: -11 ± 13.5%; P < 0.0001), ΔFVC%pred (R: 16.1 ± 11.8%; S: 0.4 ± 11.2%; P: -9.2 ± 14.6%; P < 0.0001) and ΔVC%pred (R: 12.9 ± 15.7%; S: 1.5 ± 12.1%; P: -6.1 ± 13.2%; P = 0.001) were significantly associated with radiological response. A significant correlation was observed between ΔFEV1%pred (r = 0.46, P = 0.01), ΔFVC%pred (r = 0.43, P = 0.02) and % change in linear tumour measurement. ROC curve analysis using dichotomized radiological response (P/S vs R) as classification variables showed AUC = 0.88 (95%CI: 0.77-0.95) for ΔFEV1%pred (optimal cut-off value: +7%, sensitivity: 83%, specificity: 82%, PPV: 73%, NPV: 89%) and AUC = 0.86 (95%CI: 0.75-0.94) for ΔFVC%pred (optimal cut-off value: +6%, sensitivity: 82%, specificity: 74%, PPV: 64%, NPV: 88%).

CONCLUSIONS

Dynamic lung volumes and radiological changes after chemotherapy seem directly related. Lung function changes could be an additional tool to better evaluate the response to chemotherapy in MPM.

Intensity-modulated radiotherapy after extrapleural pneumonectomy in the combined-modality treatment of malignant pleural mesothelioma

INTRODUCTION

Local therapy is becoming increasingly important as a part of the definitive treatment for malignant pleural mesothelioma after extrapleural pneumonectomy (EPP) because of the emergence of trimodality therapy consisted of chemotherapy, EPP, and adjuvant radiotherapy. Herein, we explore the current evidence and indications for adjuvant intensity-modulated radiotherapy (IMRT), as well as how to further improve this technique and adapt new technology in the delivering adjuvant radiotherapy in the setting of trimodality therapy.

METHODS

A systematic review of relevant studies identified through PubMed, ISI Web of Knowledge (Web of Science), the Cochrane Library, and the National Guideline Clearinghouse search engines was performed.

RESULTS

Local control remains poor despite the inclusion of conventional adjuvant radiation therapy in trimodality therapy. This can be improved by the delivery of adjuvant IMRT. However, IMRT can be associated with severe pulmonary toxicity if the radiation dose to the remaining lung is not kept to a very low level. This is especially true when patients are receiving chemotherapy. New advances in technology can allow for lower doses to the contralateral lung, decreased treatment delivery time, and improved target dose coverage.

CONCLUSION

Excellent local control can be achieved through adjuvant IMRT after EPP for malignant pleural mesothelioma. Severe pulmonary toxicity may be avoided by setting stringent dose constraints for the contralateral lung. This can be aided by the advances in technology. Post-treatment surveillance may be reliably conducted by periodical [18F]-fluorodeoxyglucose-positron emission tomography imaging.

A Multimodality Imaging Review of Malignant Pleural Mesothelioma Response Assessment

Assessment of response is important to interpret early phase clinical trial results and to guide individual patient management. In malignant pleural mesothelioma (MPM), the circumferential growth pattern of the disease, the presence of pleural effusion and atelectasis, and the common use of pleurodesis make this a challenging task for imaging specialists and clinicians. This article reviews the current evidence for radiological and positron emission tomography (PET) response assessment in MPM, and the pitfalls and challenges in its application. Current research and future directions in radiological and PET response are discussed, including the use of novel radiotracers.

Multimodality Imaging Review of Malignant Pleural Mesothelioma Diagnosis and Staging

Early diagnosis and accurate disease staging in patients with malignant pleural mesothelioma (MPM) are essential in classifying such patients into prognostic subgroups to allow delivery of stage-specific therapies. This review addresses the current status of multimodality imaging in the diagnosis and staging of MPM. Clinical, research, and future directions in computed tomography (CT), magnetic resonance imaging, and PET/CT diagnosis and staging of MPM are discussed, including the use of novel PET probes. The article concludes with important take-home messages summarized as the pearls and pitfalls of each diagnostic modality in the diagnosis and staging of patients with MPM.

Computerized segmentation and measurement of malignant pleural mesothelioma

PURPOSE

The current linear method to track tumor progression and evaluate treatment efficacy is insufficient for malignant pleural mesothelioma (MPM). A volumetric method for tumor measurement could improve the evaluation of novel treatments, but a fully manual implementation of volume measurement is too tedious and time-consuming. This manuscript presents a computerized method for the three-dimensional segmentation and volumetric analysis of MPM.

METHODS

The computerized MPM segmentation method segments the lung parenchyma and hemithoracic cavities to define the pleural space. Nonlinear diffusion and a k-means classifier are then implemented to identify MPM in the pleural space. A database of 31 computed tomography scans from 31 patients with pathologically confirmed MPM was retrospectively collected. Three observers independently outlined five randomly selected sections in each scan. The Jaccard similarity coefficient (J) between each of the observers and between the observer-defined and computer-defined segmentations was calculated. The computer-defined and the observer-defined segmentation areas (averaged over all observers) were both calculated for each axial section and compared using Bland-Altman plots.

RESULTS

The median J value among observers averaged over all sections was 0.517. The median J between the computer-defined and manual segmentations was 0.484. The difference between these values was not statistically significant. The area delineated by the computerized method demonstrated variability and bias comparable to the tumor area calculated from manual delineations.

CONCLUSIONS

A computerized method for segmentation and measurement of MPM was developed. This method requires minimal initialization by the user and demonstrated good agreement with manually drawn outlines and area measurements. This method will allow volumetric tracking of tumor progression and may improve the evaluation of novel MPM treatments.