Lymph node metastases in diffuse malignant peritoneal mesothelioma

Background: Improved survival has been reported for diffuse malignant peritoneal mesothelioma (DMPM) treated by surgical cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC). The significance of lymph node involvement in this disease is still poorly understood. Methods: Prospectively collected clinical data on 83 consecutive patients with DMPM undergoing surgical cytoreduction and closed-abdomen HIPEC with cisplatin and doxorubicin were reviewed. Clinically suspicious lymph nodes were submitted to pathological examination. The impact of nodal involvement on survival was assessed by multivariate analysis; 14 clinicopathological control variables were tested. Results: For the overall series, median follow-up was 52 months (range 1-126 months) and 5-year overall survival (OS) was 49.5%. Lymph nodes were submitted to pathological examination in 38 patients, being positive in 11 and negative in 27. Lymph nodes were not clinically suspicious and not sampled in 45 patients. Iliac (n = 7) and paracolic (n = 2) nodes were the most commonly involved nodes. OS was 18.0% for patients with pathologically positive nodes and 82.5% for those with pathologically negative nodes (P = 0.0024). On multivariate analysis, pathologically negative (versus positive/not assessed) nodes [hazard ratio (HR) = 2.81; 95% confidence interval (CI) = 1.12-7.05; P = 0.027], epithelial subtype (HR = 2.93; CI = 1.24-6.95; P = 0.015), mitotic count ≤5/50 high-power microscopic fields (HPF) (HR = 5.34; CI = 1.96-14.54; P = 0.001), and completeness of cytoreduction (HR = 2.06; CI = 1.19-3.56; P = 0.001) correlated with increased OS. Positive nodes (versus negative/not assessed) did not significantly correlate with survival. Conclusion: Pathologically negative nodes (as compared with pathological positive and not assessed), along with pathological and biological features, independently correlated with increased survival following comprehensive treatment. This suggests the need for careful node sampling when performing surgical cytoreduction for DMPM patients.