Mesothelioma is a rare malignancy arising from the mesothelial surfaces of the pleura, peritoneum, pericardium, or tunica vaginalis. There are roughly 2000 to 3000 new cases of mesothelioma annually in the United States.1 Although the incidence of this disease peaked in the United States about a decade ago, its incidence in many other parts of the world continues to rise, particularly in regions without sufficient asbestos regulation.2
Even with aggressive multimodality therapy for seemingly localized disease, disease recurrence or progression occurs in the vast majority of cases. Effective systemic treatment options for mesothelioma are sorely needed. To date, there is only one agent—pemetrexed—that has received specific approval from the U.S. Food and Drug Administration (FDA) for the treatment of mesothelioma. The development of effective systemic therapies for patients with mesothelioma has faced several significant challenges.
The relatively low incidence of this cancer makes accrual to clinical trials—particularly large, randomized trials—challenging. In addition, the relative rarity of this cancer can dampen enthusiasm and limit funding from pharmaceutical companies and funding agencies. As a result, much of the clinical data in this disease consists of smaller, single-arm, investigator-initiated studies. Furthermore, comparisons of outcomes between these smaller studies are complicated by significant variability in staging systems among the trials, as well as by differences in the histologic composition of each trial, which consists of varying percentages of the three main histologic types of mesothelioma: epithelioid, sarcomatoid, and biphasic disease. Epithelioid histology consistently has been associated with a better prognosis. Therefore, differences in the histologic composition of each trial can confound useful comparisons between studies.
Another obstacle to determining treatment efficacy in mesothelioma is the assessment of tumor response: the applicability of standard Response Evaluation Criteria in Solid Tumors (RECIST) has been limited in mesothelioma, particularly with respect to serial assessments of the pleural rind. To address this problem, RECIST have been modified specifically for the assessment of mesothelioma (Table 117-1).3
Table 117-1Modified Response Criteria In Solid Tumors (Recist) For Assessment Of Response In Malignant Pleural Mesothelioma3 ||Download (.pdf) Table 117-1Modified Response Criteria In Solid Tumors (Recist) For Assessment Of Response In Malignant Pleural Mesothelioma3
|Baseline Assessment |
Tumor thickness is measured perpendicular to the chest wall or mediastinum in two positions at three separate levels on transverse cuts of a computed tomography (CT) scan. Transverse cuts at least 1 cm apart and related to anatomical landmarks are used. The sum of these six measurements defines a pleural unidimensional measure.
In addition, if there is traditionally, bidimensionally measurable disease, such as a lung nodule, the longest diameter of the lesion is measured.
The total tumor measurement is established as the sum of the pleural unidimensional measure plus the longest diameters of traditionally measurable lesions.