Malignant Pleural Mesothelioma CT Imaging: How to Measure It Correctly?

Background: Malignant pleural mesothelioma is the most common primary tumor of the pleura. The unique growth pattern of malignant pleural mesothelioma makes it difficult to apply the Response Evaluation Criteria for Solid Tumors (RECIST). Hence the need to use modified RECIST (mRECIST) criteria, as they better fit the unique growth pattern of malignant pleural mesothelioma. The thickness of the tumor perpendicular to the chest wall or mediastinum is measured at 2 points at 3 separate levels at least 1 cm apart on chest CT scans, and summed to obtain a one-dimensional pleural measurement. The same criterion has also been used to assess response to treatment. RECIST 1.1 represents a further update, taking into account new concepts such as revised minimum dimensions for lymph nodes and an approach to lesions that become non-measurable. Based on experience and published literature, the hypothesis of merging the 2 above-mentioned criteria in mRECIST 1.1 for mesothelioma and the use of iRECIST for the application to immune-based therapies (iRECIST) was considered. Purpose: Support the importance of studying pleural mesothelioma in a reliable and reproducible way, through a scrupulous methodology, applying the mRECIST1.1 and iRECIST criteria. Conclusions: Adoption of a standardized study metodology can make the study of PM reproducible and correct.