Lymph node involvement and metastatic lymph node ratio influence the survival of malignant pleural mesothelioma: a French multicenter retrospective study.

Malignant pleural mesothelioma (MPM) is a rare tumor with disastrous evolution. The prognostic value of nodal involvement is still debated. We analyzed the impact of nodal involvement on overall survival (OS) in patients treated by multimodal therapy including extra pleural pneumonectomy (EPP). We evaluated the role, as a prognostic factor, of the metastatic lymph node ratio (LNR), corresponding to the number of involved nodes out of the total number of removed nodes. In this retrospective multicentric study, we reviewed the data of 99 MPM patients. Information regarding lymph node involvement was assessed from the final pathology reports. N1-N3 patients were pooled as N+ group. The OS, calculated by the Kaplan-Meier method, was compared using the log-rank test. A multivariate Cox proportional hazards model was used to identify independent prognostic factors. For the whole cohort, median OS was 18.3 months and 5-year survival was 17.5%. N+ status reduced significantly the median survival (22.4 months for N0 patients vs 12.7 months for N+ patients, P=0.002). A lower metastatic LNR (≤13%) was associated with a significantly improved median survival (19.9 vs. 11.7 months, P=0.01). OS was not related to the number of involved or total removed lymph nodes. In multivariate analysis, only adjuvant radiotherapy (P=0.001) was identified as an independent positive prognostic factor. Metastatic LNR is a more reliable prognostic factor than the number of involved lymph nodes or the total number of removed nodes. However, it could not be identified as an independent prognostic factor.