Journal of Thoracic Oncology:
Letters to the Editor
Department of Pulmonology/Respiratory Oncology, University Hospital Gasthuisberg, Leuven, Belgium (Nackaerts, Vansteenkiste)
Department of Thoracic Surgery, University Hospital Gasthuisberg, Leuven, Belgium (Nafteux)
Disclosure: The authors declare no conflicts of interest.
Address for correspondence: Kristiaan Nackaerts, MD, PhD, Department of Pulmonology/Respiratory Oncology, University Hospital Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium. E-mail: email@example.com
To the Editor:
We read with interest the practical guidelines offered by Tsao et al.1 on how to make measurements of malignant pleural mesothelioma (MPM) by modified RECIST criteria. When we try to make a diagnosis of MPM, we usually rely on a combination of clinical characteristics, of radiological and (more recently also) nuclear imaging findings together with a confirmatory pleural biopsy and/or pleural cytology sample.2 Careful measuring of MPM tumor on computed tomography (CT) scan of the chest is crucial not only at initial diagnosis and staging but also for correct identification of tumor response to treatment. MPM may, however, present not only as a well-delineated and measurable pleural thickening but sometimes also as a much thinner, not really well-delineated rind-like pleural involvement. Occasionally, pleural involvement by MPM is only macroscopically detectable during thoracoscopy and later microscopically proven while the CT imaging does not show any significant pleural thickening at all. Differential diagnosis between minimal benign pleural thickening and MPM can indeed prove to be very challenging based on CT scan only, and recently, the additional value of the fluorodeoxyglucose positron emission tomography imaging combined with CT scan has been demonstrated.2
What we actually missed in this practical guideline by Tsao et al. were the tips to “evaluate” MPM cases with these radiologically minimal rind-like thickenings or with occasional “nonmeasurable” or “normal” pleural MPM disease. When we participated in the landmark MPM trial by Vogelzang et al.,3 measurements of MPM pleural involvement were uniformly performed using the study protocol efficacy criteria for tumor response as modified from the preexisting Southwest Oncology Group standard tumor response criteria published by Green et al.4 Briefly, in patients with unidimensionally measurable disease, thickness of pleural rind had to be measured at three separate levels on transverse CT cuts. Levels should be at least 2 cm apart from each other. At each level, measurement of up to three areas of pleural rind should be performed where feasible. Measures should not be made of pleural thickening that was less than 1 cm. Ifbidimensionally measurable lesions coexisted, these could be measured according to RECIST criteria and the measurements could be added to the sum of the unidimensional measurements. In 2004, these adapted or modified RECIST guidelines on how to measure MPM tumors were published in detail by Byrne et al.5
According to the Vogelzang trial protocol, MPM disease status could be defined not only as measurable disease but sometimes also as “non-measurable” or “evaluable” disease and rarely as “nonevaluable” disease. Evaluable disease was defined as pleural lesions on CT scan with perpendicular diameters smaller than 1.0 cm, as has been also detailed in the practical guidelines by Tsao et al.1 In this category of evaluable or non-measurable rind-like pleural thickenings also pleural thickening secondary to previous talc pleurodesis may be classified. It is important, however, to document evaluable MPM disease at baseline and during treatment, because the evolution of both measurable and evaluable disease needs to be taken into account for future response definition.4 This also holds partly true for nonevaluable MPM disease (like pleural effusion or ascites) because, for objective complete tumor response, nonevaluable MPM disease needs to be completely absent. In MPM patients with nonevaluable disease only where no complete response is present, no other MPM disease status can be assessed.
As a suggestion, therefore, and in expectation of possible newer evaluation tools for MPM,2 we would like to propose the authors to provide clinicians with a complete practical guide on how to make radiologic measurements and evaluations of all possible MPM cases, presenting mostly with measurable, sometimes non-measurable, and occasionally with evaluable-only pleural disease.
Kristiaan Nackaerts, MD, PhD
Johan Vansteenkiste, MD, PhD
Department of Pulmonology/Respiratory Oncology
University Hospital Gasthuisberg
Philippe Nafteux, MD
Department of Thoracic Surgery
University Hospital Gasthuisberg
1. Tsao AS, Garland L, Redman M, et al. A practical guide of the Southwest Oncology Group to measure malignant pleural mesothelioma tumors by RECIST and modified RECIST criteria. J Thoracic Oncol
2. Nowak AK, Armato SG, Ceresoli GL, et al. Imaging in pleural mesothelioma: a review of imaging research presented at the 9th International Meeting of the International Mesothelioma Interest Group. Lung Cancer
3. Vogelzang NJ, Rusthoven JJ, Symanowski J, et al. Phase III study of pemetrexed in combination with cisplatin versus cisplatin alone in patients with malignant pleural mesothelioma. J Clin Oncol
4. Green S, Weiss GR. Southwest Oncology Group standard response criteria, endpoint definitions and toxicity criteria. Invest New Drugs
5. Byrne MJ, Nowak AK. Modified RECIST criteria for assessment of response in malignant pleural mesothelioma. Ann Oncol