Does size matter? -a population-based analysis of malignant pleural mesothelioma.

Background: The 8th edition staging system for malignant pleural mesothelioma (MPM) has been proposed. The size of tumor is not taken into consideration. We intend to elucidate the prognostic value of the size of MPM and evaluate the current staging system via the data of SEER database. Methods: All cases of primary MPM were identified and extracted from the SEER database during the period of 2004-2016. The endpoints were overall survival (OS) and cancer-specific survival (CSS) which were analyzed using Kaplan-Meier method. Log-rank test and Cox regression were utilized to identify the prognostic factors. Results: A total of 2,138 patients were included in the primary cohort. The 1-, 3- and 5-year survival rates of MPM were 39.4%, 11.8% and 3.8%. Older, male and advanced stage patients accounted for larger proportion of the cohort. Besides tumor extension, lymph node involvement and metastatic status, tumor size, pathological type and differentiation grade were significant prognostic factors. In the stratified analysis of tumor extension, size is a significant prognostic factor in T2 patients and indicates inferior survival outcomes. Surgery, chemotherapy and radiation can increase both OS and CSS in MPM patients. Triple combination treatments showed a superiority to other treatments. Conclusions: Tumor size matters in the prognosis of MPM especially in the early stage of MPM patients. The adjusted TNM staging system incorporating tumor size has better accuracy than the 8th edition IMIG system. However, some stages had not been fully identified. More cases of early stages are warranted for essential revision.